Is medium size UTH adequate for 24x18 enclosure?

[RBJersey]

I purchased the medium Zoo Med UTH which measures 8x12. Tank is Exo Terra medium low which measures 24x18. If I do the math it's a little under 25% of the total floor space. just wondering if I need to go with the large UTH which measures 8x18.

 

[mrhellboy218]

If it heats up the tank right then I'd just stick with it, usually the heat mat should be 1/3 of the tanks floor but 25% of it sounds ok