The difference in STA has nothing to do with weight balance. Both bikes have the same chainstay length and nearly identical wheelbase. Your body should be placed in the same position relative to the BB on both sizes. I'm only an inch taller, but my legs are 3 inches longer. My wingspan is also about 2 inches greater than my height. I could ride either size, but the steep sta on the 49 would move the top of the seat post about 18mm further forward. I might get my saddle back far enough with a 32mm setback post. I would use a 25mm setback on the 52. I wonder how you select such a forward position - KOP maybe? I select setback based on my balance over the saddle, not any knee to pedal relationship. With your shorter saddle height, that alone moves your saddle quite a bit further forward.