I was going to suggest the same, maybe the 40watt isn't what you needed? When I purchased my T10 which is 4x2x15 I think, ProProducts recommended a 75 watt which I've never had an issue with and maintains my temps without having to run non-stop. The other thing I was going to ask about was are you sure this isn't an issue with your chosen thermostat? I'm unfamiliar with the model inkbird and with the brand ingeneral to be honest so pulled the one you mentioned up on Amazon. I didn't dig too far into the reviews, but I didn't see anyone mentioning these being used in reptile enclosures, and there were some mention of it not being UL listed. There's also some mention of these needing to be calibrated, and I'm just wondering if maybe that's where your issue is rather than with the RHP itself.