I think the weight and warhead difference of long range sam vs a bvr missile converted into sam is important. This M1 missile tenders had shown 2 different warheads, 30 kg and 60kg class. Astra in comparison has a 15kg warhead. So if a bvr is converted into a sam, it will need to up that aspect too and will need to have a redesign.
Also bvr missiles, most of those pull up post release and drop down onto the target at a much later terminal stage when target is locked on, else it would not be able to sustain the long range engagement. What altitude does that happen at, must be over 15km at least? I would guess pretty high alt for its coasting part?
Astra can pull higher Gs than missiles like Barak, so Barak carries a larger warhead to compensate.
Dual pule takes care of that. As for altitude, it can be adjusted based on fire control information.