Add a vent hold in the booster, near where the sustainer motor will be.
Did not have vent holes the first time i launched. Sustainer did not light prior to the booster popping off, and had to rebuild the sustainer from the fin can up. Added a vent hole, and the two subsequent launches have staged fine.
Maybe that is only coincidence, but the vent hold should not hurt anything.
Also a 6' x 6" streamer has worked well for recovery for me, for a D12 to E9 launches. A lot less walking to do.
The stock chute makes it darn near hover in the air. I think I got about half a mile of drift out of my D12-E9 launch. Sheesh. Add a spill hole or go to a streamer as mentioned. I think I'm going to do streamer.
Oh, do the vent holes too. I had a literal lawn dart the first time I flew mine. Sticking out of the ground happy as could be. Funny as hell pics. Of course, mine had the magic disappearing motor... The sustainer motor was just.. gone... Not in the rocket, not on the ground, not in my range box, nowhere to be found. I won't say for sure that I put it in, but I sure think I did... weird.
Oh yeah, i forgot... The stock parachute is some GIGANTIC parachute (32"). Waaaaaayyyyyyyyyyyyyyyyyyyyyyyyyyyyyy to big. I used a 15" or 12" chute, on the second flight. Still took 50 seconds to come down.
I can see the idea of just popping the nose working. Fin can is very solid. Streamer still aids in tracking the descent of the rocket.