Yeh I noticed your frame has a steeper seat angle on the larger size, which makes sense since the seat will be further back the more you put the saddle up.
Yes. For the same saddle height, a rider on a larger frame of ours will be further forward of the back wheel.
Which will make the bike climb better when seated (without wheelieing).
Stood climbing will be essentially the same (as distance from BB to rear wheel is same).
It’s only quite a small difference, but half a degree on the seat angle is about the same as 6mm of movement on the saddle. But 6mm movement on the saddle does make a difference in making the front end stick down on climbs (or not).
Setting knees over pedal spindles or trying to get a longer seated position by running a layback post just throws weight too far back.
To my mind seated position should be optimised towards steeper climbs which on a long travel bike will give a “seat forward” feel.
Riders trying to duplicate seated length from bikes of ye olde days, or heaven forbid, their road bikes on a long travel bike will end up with something that won’t work well in rumpy bumpy terrain.
Of course for singlespeeds, it makes no odds at all, and infact rearward weight bias is good (especially for offroad fixies), as climbing is not affected, as you can’t really climb steep stuff in the saddle on a singlespeed.
So if that layback post if for a singlespeed, it has my blessing 😉