Humidor too small?

[PCR]

I noticed something peculiar this evening. I was taking an inventory of my cigars that are in my 15"x12"x 10" humi. I have about 40 cigars in it, the cigars on the top shelf (approx 12 cigars) are more moist that the bottom cigars. I have 4 oz. of Shilala beads (2 oz. on top, 2 in bottom). I am thinking there may not be enough air circulating? RH ~ 64-68 @ 65 F temp. Held steady all winter.
Any help would be appreciated, thanks.