RE: With an Anglo and a suitable position of the handle most individuals can manage 30 Anglo keys with a fixed hand and that is the best when possible since instrument control can only benefit from better stability. The individual length of the little finger may be a limiting factor reaching the most distant buttons on 3rd row for sure but a higher rest located closer to the keyboard at the little finger side deals with that.

I'm struggling with the concept of "an individual length of a little finger"
My little fingers are the length that I was were born with. I have no problem. If in some strange way, they changed length dramatically, I'd play differently. But, No, they seem pretty motionary at the moment. So, i'll stay with the lovely box that I'm playing. It suits me fine..
If my fingers start to grow, I'll let you know.