Quite frankly, a 1½" wide bamboo backed purpleheart bow is just begging for chrysals. You asked for a design that doesn't lend itself for chrysals. Well, we gave you advice, but backing a compression weak wood, while leaving it narrow, certainly wasn't on our list of recommendations
This would be my advice when using purpleheart, which is very prone to chrysals:
-Do not use bamboo for a backing; use a lighter wood such as maple or ash.
-Trap the backing, and leave the belly flat.
-Make the limbs at least 2" wide.
-Let it bend through the handle.
-74" for a 28" draw.