I got the one from Walmart like the picture someone on here posted 12"x14"
and it has uneven heat also but every heat pad I have ever own has been like that. The temps on my hot side run around 88-94 depending on where and how the bp has moved the reptibark.
I don't see how you guys keep yours on med or high, mine becomes way to hot and I have papertowels down then reptibark and I have mine set on med with a dimmer switch set at about 1/2 way . If I put on low or med temps rise above 100 without the dimmer switch.
My set up is a 20 gal breeder tank so maybe thats why just a smaller enclosure.