HI,
The thing with monitors is to give them lots of choices...I agree, I try to give all monitors a spot that is 130 degrees F or so, but I also have a side of the cage that is 70 or so. Frankly I don't even really worry about ambient temps with monitors...I just give them lots of different temps in different areas and let them decide what they want - they certainly know better than me. My animals use both hot and cool areas and all in between at different times depending on what they want. Both areas have plenty of hide spots, and there is deep substrate all around so they can burrow.
Feeding lots and being active is certainly a good sign, but in your setup I would strive for a little more gradient in temps, and let the monitor decide what he wants. I would also recommend observing a lot at different times - dusk, dawn, night, day - and see what the animal does. That will teach you more than any web site or care sheet.
Good luck,
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Phil Black
www.VaranusWeb.com