FWIW I don't do any heat bending before glue up and I can easily turn a tri-lam into a recurve.
I think the reason is that I'm using a solid form that I clamp the lams down onto as opposed to the centerpost, midlimb post, and tip post setup ... Just a thought.
I do like the 5 post setup though and I actually have a setup like that that mounts to the flat side of my form too if I wanna free-ball it a bit more.