From my understanding 85 is optimal. 90 is "safe", but 95 is "way too hot" for a corn. So long as the cool side remains 70-75 though it should be okay.
My concern is you said you're using the UTH. If he burrows under the substrate and lays directly on the glass, you could be looking at some burn problems if you're not careful. I recently (through the advice of the excellent people here) put a ceramic tile overtop of the UTH. It works great so far, but it can still get hot (according to my cheap thermometer), so I may put a thin layer of substrate between the glass and the tile to lower the temp. I'm waiting until the winter comes so I can adjust accordingly.
But I digress... 87 is okay, but keep an eye on it.