I'm not doubting that you know what you're doing. Looks like you do great work.
I've ran a set of 1508's in a 2.5 cu box with 17" port per cu tuned to 34 hz on an m2b. Suspension on the 1508's are pretty stiff. I've never had issues with them bottoming out but did get them stinky from time to time.
I'm sure that they will perform well in current box.
I'm waiting for the super 8's to be available. Will be running 3
in 4 cu on an m4 with an 8" aero.