Umm...
They don't make a PPQ compact.
The only "compact" version of a duty sized pistol that Walther currently makes is the P99c AS.
I have three P99s, one of which is the compact "c" version.
I use Trijicons on the full size models and Meprolights on the compact.
Mep used to make two different sight sets for the P99 (and by extension the PPQ as they both take the same sights). One was for the "full size" and the other was for the "compact". They dropped the model number for the full size and now only sell the one originally for the compact P99.
The Trijicons are for the full sized models.
I have verified this with my pistols. I put the Meps on a full size and they definitely changed the point of impact compared to the Trijicons. On the C model P99 the Meps shoot to point of aim.
I should add that I use the original Walther "combat hold" sight picture, which is number 3 in the chart posted in your link, as that is how the stock Walther sights are regulated. What the chap on the other forum is doing us using the P99c sights to make his full size PPQ shoot to a different point of aim than the stock sights, which is what they will do.