When you add reflex you also need to allow for more width. Thoe wood has to bend more so it has to be thinner.
Exactly. Narrow bows with curves or reflex wart to bend sideways to some degree, and are trying to, even if they don't. wider and flatter gives them only the option to bend front to back.
Reflex doesn't shorten the draw potential,it just increases the chances of blowing or overstraining the bow, and must be handled judiciously. A couple, even a few inches of reflex is a great place to start. More than that, and I will deflex at the handle, or pull some reflex out of inner or midlimbs while heat treating.