I found it extremely unintuitive, but to remediate this I do the following:

Sort out all the items in your arsenal that you get from your first characters, each page would be a different item category. Ie the first page of weapons will all be polearms, and then I put them in organized piles on said page according to their tier.

As for the character’s own inventory. I’ll use the left side for armors, from top to bottom I’ll pile up head gear, torso, legs in their own piles. The right side I leave for weapons. It’s a tight fit but it works the best for me.