I would also suggest an inch is a bit much. I love ultratherms. They are the best available IMO. The lower density heater (like the 17 inch flexwatt 8w) it simply will not get as hot as a regular pad. Mine unregulated in 80º room temps has never hit over 100º. They are ok on a glass tank I have used them with no issues. (THEY need a T-Stat) the only issue is if the room drops its temp too much the hot spot drops too... I find that at 70º mine runs 100% power most of the time to hold 90ºF. Unlike the zoo meds (unregulated hit over 160º) I have that run 30% under the 70º room temps. I would push them simply because t-stat failure is always an issue but not getting temps over 110º increases the margin of safety a lot.
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http://www.reptilebasics.com/ultratherm-faq
I would not suggest using ANY heater with out a T-stat even regardless of what RB says.