Iam guessing that particular Bow design,would have more effect on Brace ht. "sweet spot" than differences in bow lengths. I do think diff. string materials, number of strands is going to cause varitions in brace ht. sweet spot.
I really don't know, any of this for sure. Also,individual shooting styles, particularly method of release is likely to have an effect on what the "sweet spot" turns out to be. I think you just have to experiment for yourself w/diff. equip. and string material. I don't think its a one size fits all,kind of thing.