I've played enough with different LPs and thought through lessons learned that an analysis of the differences will probably be accurate.
Spin reversal (vs geometry)
For the most part for all current LPs, reversal entirely on stroke/speed against the surface than some innate property of the rubber.
They all share the same geometry: the 1.1 ratio cylinder, the biggest diff being how tightly packed. The softer/tackier rubber compounds closer together will have a bit less reverse potential but there's order magnitude difference in friction between contacting the sides vs the "top-corner". Thus every rubber has its range of modest friction against the tops, to low friction against the top edge, to medium friction against the sides.
IMO the confusion here lies when players evaluate LPs against each other with the same stroke. So a flexible (easy to bend) pip will be in low-friction range with a light chop, while a stiffer pip will barely bend and be in the modest friction range. Same for a heavier chopper who'll think the stiff pip reverses more than the flex one which'll be in the bent/medium-friction range. This also isn't a one-dimensional problem because some players evaluate more for chop/block motions rather than distance/stroked chops, and some still have fwd/high-throw chops and some vertical/low-throw strokes.
Contrast this vs frictionless LPs, which will have much lower friction throughout the range, ie be less effected by how much bending takes place. These will be easier to use and generally have more reversal throughout.
The main takeaway here is that comparison which don't control for these vars aren't terribly useful and might as well be arbitrary for anyone but that given player.
Rubber compound type
Just as traditional chinese vs euro/jap inverted has its own characteristics (chinese tackier natural rubber vs more elastic synthetics) there some difference between their respective LPs since they're generally made with similar "kind" of compounds as the inverted.
This presents some parallels like "mechanical elasticity" of the pips, but their function is entirely different since this usefulness for top-top rallies isn't the same for reversing (or generating) spin with pip sides.
Principles would dictate that all things equal grippy but not tacky pips reverse more on blocks, while tackiness helps stop the ball and turn the spin around when the sides are engaged. The popular Japanese chopping pips tend to be soft to absorb speed and bend easily for the sides to grip. Meanwhile harder pips provide better attacks and reversal on active strokes into the ball, allowing greater range of strokes at the table using different parts of the pip.
Also worth noting is that just as the compounds for chinese inverted topsheets have changed over the years to become more elastic and less tacky (for the same models) the same changes are likely for their LP sheets. Another related issue in the same vein is that chinese LPs are notoriously inconsistent between batches not only in compound specifics but actual mold shape. Eg. some Globe 979, DF 1615 are flat and some are texture topped.
There generally greater variety of sponge used in LPs than inverted (all max elastic), and I believe most of the more drastic "differences" users detect between them are due to sponge rather than inherent top-sheet characteristics which we've seen depend more on the stroke used.
For example, the ubiquitous Palio 531A is middle of the road chinese LP in OX but comes a fairly fast 0.7mm sponge that makes it much more offensive (and hard to chop on even medium blade). Contrast to inelastic foamy 1.0mm+ sponges which absorb impact and are slower despite the thickness.
Without sponge, the pips "break" more drastically on an angled chop and the intersections between the ranges above become more distinct. But without the moveable backing, it's also harder for them to bend over completely and the low-friction range is extended.
Thus the easiest way to engage the pip sides (if such thing is desirable, for most friction) is a soft/flex pip on a soft thickish sponge.
Ribbed vs flat top
There was also some discussion on the first page of ribbed vs smooth. This diff isn't going to matter on any stroke that bends the pips (ever moderate contact at an angle). For everything else consider that total friction is a function of contact surface given equal friction-coefficient. On contact from an oblique angle (ie light brush shot) a ribbed surface (with parts sticking out) is going to present more surface area, whereas for a shot parallel into the pips it will present less (the sticking-out parts are less surface than a flat one) so it will reverse spin more on blocks.
Thus the answer here is that it depends on how it's played. Flat surface will produce more no-spin rather than reversal on pure blocks, etc. To apply the info above, this changes on chop-blocks which bend the pips somewhat and this distinction goes away (and therefore any statement about ribbed vs flat when evaluated with a chop-block is pointless).
This shouldn't be significant, ie placebo effect. Each pip interacts with the ball individually, and the area of interaction will always be a circle which contains on average the same number of pips regardless of orientation.
In terms of topsheets, most of the current chinese LPs tend to be more similar than different. There are some minor distinctions like textured vs flat top, softness, and packing closeness (388-1/979/1615 are sparse, Neptune/531A denser, 755 in between, etc), but how these effect the game is more closely related to the player's stroke than any inherent "reversal" of the rubber. If anything, the great variety of sponge backing (esp standard vs foamy) is what makes for the significant variations in impressions.
In light of all this, EJs looking for the "perfect" pip to supplement their existing strokes can't depend much on other's reviews, but for new users just about anything works with some adaptation. Just take care not to get an harder/elastic attacking sponge for a defensive game.
....this is a brilliant post. Well done sir. Accurate and clear.
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