2x6 WSE Arch - building the baffles

hi all - I recently bought a new 2x6 Leader WSE arch to use with my (older) Grimm Lightning raised flue pans. The flue pan is 2x4, stack is 10" diameter and 15' tall, and no blower on the arch. I have the Leader WSE Manual and bought the recommended arch board / brick / vermiculite / cement. The manual seems pretty straight forward regarding the arch board and bricking, but i was hoping for some advice on building the baffles and insulating / filling in the back half of the arch. How many baffles would everyone recommend, given the arch size and raised flue setup? I've read that the draft is very sensitive to how much gap i leave between the stack plate and last baffle. Is that true? I am thinking to build up one baffle with brick, filling it in with vermiculite, and layering the whole thing with fire blanket. Has anyone tried that? Any and all advice welcome, thanks.