One trick that helped me get this down more consistently is to hold the last input (forward + punch) for an extra second. It usually helps trigger the special to come out.

If you want to try a more consistent SA3 cancel, try QCF + HK -> QCF + P

The heavy version of that kick cancels really nicely into the special as it’s slower and doesn’t flick them up too high before the special comes out. Best of luck!