It is really not a good idea to have the tank over-hang. It will cause pressure points, which over time may crack the tank, or rip a seal out. Also, I know you said there is nothing blocking the heat lamp, but is there anything in between the UVB BULB, and the basking spot?(like glass, or the plastic cover of the slimline fixture, or the covers for the tank?) If there is ANYTHING in between it will block the UVB rays.
Once again, awesome set-up, and I can't wait to see the above tank basking spot!!

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RES's
Tank, SCL 3.75in.
Diesel, SCL 3in.