Look at JBL's kit.https://www.midwestspeakerrepair.com...le_16_15_1.jpg
I've cut mine around the same specs (found other pics at that time) and it pushed quite hard on the dome. Scary but sound was just great. And is still! Just to barely touch is not enough, you want a tad amount of pressure.
http://www.audioheritage.org/vbullet...l=1#post358810
Good luck!