I got a new helmet...same make/different model from past one.  I've always fit XL.

After an hour or so of riding, I get a headache.  Two possible solutions are to order a liner for an XXL which is the same size shell but thinner material.  Keep wearing the helmet and see if the padding breaks in more.

Fit is snug but not uncomfortable.  I'm wearing it as I type with the stopwatch on my phone running to see how long I can wear it comfortably.

I do wonder, as I think it's happened before even with a broken in helmet....

If the weather is hot (or you get hot/dehydrated), does your head swell larger or something similar in effect that would make a helmet less comfortable and trigger headaches?

I've tried on different Arai models and they do fit differently in the same size. My current Arai is all day comfortable until it gets into the upper 80's then I get a "frontal" headache after a few hours.
On the other end of the temperature range (35 and below, at speeds over 60 mph) I get a brain freeze type headache, but that could be the bike aero.

You would think they're all made the same but there's a lot of manual labor into helmets.
Add to that two designs, even from the same manufacturer and you get a different fit.
There is also the old shoes vs new shoes thing here. I say give it a while. If it doesn't improve, some retailers do offer fitting your helmet.

Do you need a haircut??

I could say yes, but I keep it so short I’m just about bald.

Garry, I don’t want to keep buying helmets.  I like the idea of adjustable fit, and perhaps more should do that, but I’ve been an XL for all this time, so it’s either an issue of breaking this one in or something changed in manufacturing.  This new one (HJC i90) was picked so my Sena speakers could mount within without modifications.  Two changes from my last one (SY-MAX) are an issue for me...(1) visor deployment is a slider near the chin on the left.  It’s not easy to operate.  Prior design was on the top of the helmet and spring loaded.  Deploy and lock...press button to retract.  I do not like the new setup which is 100% manual.  (2) the front “locks” more securely (which seems an odd complaint), but when it latches, it hugs the face slightly more snug than when the front is open.  I wonder if that slight increase is why I’m having this issue.

In any case, I ordered the XXL pad set.  So long as it doesn’t make the helmet too loose, it will fix the issue.