Hi, I'm not and Helmet expert, but by my short experience, (I have built 4 ANH helmets only) , once I get the correct face-cap alignment, I used magnets and clamps, make the holes and place the rivets to affix this main two pieces and start to align the ears using photos and trim little by little the zone where there is too much gap. remember, they're no perfect fit. take a look to the following hero helmet photos.
Another suggestion is to try to take the helmet photos showing it complete from at least one meter of distance and a crop the picture to have a closer view and a correct perspective, this is so helpful for us to have a better idea of your progress.
Hope this can help.
cheers