A rider on a mtn bike is like a tower on wheeled platform. Where on the platform do you think is the optimal place for the base of the tower, to get the setup to handle how you like over obstacles and terrain? Dead center? Slightly rearward? How would you describe it in terms of weight on the forward and rearward wheels? 60% rear, 40% front? 55 rear, 45 front? 50-50?
I've done this test on my own stable of bikes, and found that a number of them had ~67.5% rear and ~32.5% front, when sitting in the saddle. When standing up in a neutral/pedaling position, that shifted to ~52.5% rear and ~47.5% front. Cruiser bikes exaggerated this pattern, with more than 70% weight on the rear when seated, and less than 50% weight on the rear when standing up. XC hardtails were very similar to the cruiser bikes. The Ibis Ripley V1 was close to 50-50 out-of-the-saddle in size M. From my own preferences, trying to pick which one out of all the bikes in my stable that I liked the most for bike parks and "freeriding", I found that the ones which approached 60% weight on the rear out-of-the-saddle felt increasingly radder.
A rider that is more free to move on the bike, works better to absorb impacts, like how tuned mass dampers reduce oscillations/swaying in skyscrapers. To take advantage of this, why not put ther rider in a position to have more freedom of movement, being centrally located, rather than forced rearward? The BB represents the place where the rider is placed on the wheeled platform, if they have a heavy-feet and light-hands riding style. The straight-forward solution to this is to adapt the bike's geo to get this sweet-spot balance naturally, rather than have the rider move themselves into it.
Can estimate the weight distro by simply finding out where the BB is in relaton to the wheel axles. On the geo chart, I can figure this out by comparing the chainstay length to the wheelbase. A 415mm chainstay with a 1100mm wheelbase will feel too forward biased, with less than 55% weight on the rear. A 415mm chainstay with a 1200mm wheelbase will feel too rearward biased, with more than 60% weight on the rear. It'd be great if you like having your wheel up in the air, but you'd risk front wheel wash-out and would have to compensate with a super grippy tire like a Kenda Hellkat. With 1150mm wheelbase, the 415mm chainstay results in 57.5% to 60% weight on the rear. If 435mm chainstay were as short as a designer could make a bike with 160mm travel, with 29er wheels, they should tweak the wheelbase to get the balance right, with 1230mm getting similar balance to the 415mm CS and 1150mm WB bike.
If anyone believes what I'm saying, it should then imply that only certain sizes hit the optimal balance, due to how short-sighted designers size their bikes. The brands that have tuned chainstays to change by 4-5mm between sizes have the right idea, at least for out-of-the-saddle handling. The next step is to reduce the massive weight shift between standing and sitting by getting seat tubes steeper, which affects things like how likely you are to get a rear flat when you're lazily sitting in the saddle while crossing a large rut perpendicularly (square-edged impact) and how much the bike's rear susp squats when climbing (contrasting with how firm it feels out of the saddle). Steep STA shouldn't be a problem now that dropper posts are more of a norm, able to get the saddle out of the way to move around easily. Also, riding style determines the "sweet spot"... some people genuinely prefer the defensive position and find it hard to break out of habits, so that 50-50 balance of the Ripley might be "comfortable/natural" for them. I'm just basing recommendations off a generalization that someone interested in bike parks and areas with significant elevation change would be interested in balance tuned for getting rad, from a mechanical perspective, rather than attributing opinions to Roxy Lo, who is short and designed the Ripley.
P.S. angle tweaking headsets and fork length extending can give you about 1" in extra wheelbase, equivalent to going one size up in terms of fore-aft balance.
If this is your first suspension bike it's going to be amazing no matter what.
