The real issue with the nose cone coming off at apogee isn't drag separation, but more likely shock from the payload section reaching the end of the shock cord. If the shock cord is too short, the nose cone may have enough momentum to loosen itself and separate at apogee when it reaches the end of the cord during deployment. This is especially true if you have any significant nose weight or if you use excessive ejection charge. I had this happen on my first few DD flights due to nose weight and loose fit of the nose cone. The nose didn't feel "loose" by any means, and wasn't that easy to separate on the ground, but consistently came out at apogee. There were no real negative consequences to main deployment at apogee, just a longer walk for recovery.
After adding shear pins, the problem has been solved, deployment has gone as planned. Shear pins are cheap and easy to work with, and I recommend them. But don't forget to have a long-enough shock cord (3 times rocket length is the rule of thumb I have read here, others go longer) and ground test, ground test, ground test!
NAR, TRA L2
Member: CMASS, MMMSC
"I haven't slept for a week because that would be too long." -Mitch Hedberg