Can't put a picture up...But you may have read an old post of mine.

I rode for months having to lock my helmet on the bike before I finally found out that it actually fit in the side bag!

I have a 5xl HJC full face, and I found that it will only fit into the left side bag...
stand in front of the left opened bag. Your helmet must go in with the face of it towards the front of the bike, the lid when you close will be touching the top of the helmet (another way to put it...the helmet opening will be facing towards the tire). I also make sure it is towards the rear as far as it will go. when I close the lid it just barely touches and it easily closes...there is no forcing to it at all. I do use my finger tips to help keep the helmet pushed flat up against the back just prior to closing.

Now a HJC 5xl is as big as they come...so I thought. My be true for the inside diameter, but maybe not for the outside. On one of our rides I tried to help another out with this, his was a full face Shoei, but only a large...and it would not fit.
I too also tried the right side bag, but for me...that was not even close to fitting.

Good Luck!