Thanks everyone!
I am unable to put a heater near it, I believe, because of the corn. I don't want her overheating.
Just to add, the corn's UTH is on the side closests to the BP's side (right next to the divider).
As for the BP. The ambient is 77.5F, as I've mentioned. There is no different between 'warm' and 'cool' side unfortunately. I have only a thin layer of substrate, as I noticed it difficult for heat to get past the PVC. The UTH does no job at all of heating the interior of the tank, apart from the hot spot... which is why I am concerned!
I am hoping that if (and when?) the mulch dries more it will warm up a little as well.
I do have another option, but I don't know if it'll work. I have an extra (small) UTH laying around. If I were to get a double-plug in going on my corns thermostat (which hovers around 83.5F) could I add another UTH to the BPs vive? Sort of in the middle.