I think I posted about this a couple years ago when I first got my Rift. It's still a problem for me. I have tried everything.
I perceive the relevant skull factors to be:
1) I have a strong occipital bone structure (strong rear skull).
2) I have weak zygomatic bones (weak cheeks).
In application I have the following problems:
1) My facial interface almost entirely rests on my forehead due to my weak cheeks. This causes impingement of the supraorbital and supratrochlear nerves thereby numbing my scalp which is extremely uncomfortable.
2) More generally there is too much tension being placed on the top strap and too little on the side straps. I feel that the ergonomic design of the Rift depends on adequate cheek contact which I do not have. Without cheeks everything becomes top loaded.
Possible fixes which have failed:
1) Raise the height of the rear mount to bring the facial interface more into contact with my cheeks. This doesn't work because my strong occipital demands a certain rear mount or it doesn't anchor.
2) Tighten the side straps. This only exacerbates the forehead impingement in exchange for still inadequate cheek contact.
3) Tilt the ocular part of the HMD about the side hinges. This doesn't work because the side hinges are too limited in their range of motion. If they had a wider range then it would probably work. But too much tilt would probably upset the alignment of the display to the eyes so this is probably a bad approach.
4) Aftermarket facial interfaces. I have yet to find one with the strong cheeks that I need.
Fixes I haven't tried:
1) Cut notches out of the forehead foam where the nerve branches are. It may come to that. I just hate to physical modify the Rift in a permanent way.
2) Fabricate a custom interface. This would probably take the form of additional layered cloth being affixed to the bottom half of the interface to create thicker padding in the cheeks. I just want to avoid permanent modifications. It would be easy to use adhesive but that's permanent. Without adhesive it would be difficult to anchor a partial interface.
I don't know if this will help you but I'm putting it out here because it's fast, easy and reasonably cheap to try. It may also help someone else as it helped me with some headset issues I have.
I found that by simply wearing a baseball cap backwards and putting my headset on over it I can make numerous adjustments to the comfort of the headset by simply shifting the baseball cap. Doing this more than doubled the amount of time I can wear the headset comfortably.
