uth won't really work under this tank. it has about 6-8" of substrate including lava rock and false bottom. hence them being on the side. other than blocking heat loss, it really didn't do much, especially for belly heat. but the whole time I've owned the inhabitant in question he has had side mounted UTHs with no negative side effects.
I could find a way to block off that left side with something else. I have a few gorgeous pieces of, like, 15 year old sun dried black walnut wood that would work well.
this might just be the excuse I need to plumb an eth into the water feature that is soon to come.