I've never used apitong, but in order to glue the pieces up into a deflex/reflex profile, they need to be thin enough to bend with relative ease. I usually make osage 1/2" or less thick. In fact, I've made 70 lb d/r bows with 1/2" thick osage slats.
If you have the capability to do it accurately, it also helps to pretaper the slat from dips to tips. It makes the outer limb thinner allowing it to bend easier, and can allow the limbs to take on a more even reflex along their length during glue up. 1/8" of taper in the limb area is generally sufficient.