The purpose of a second row of heat tape.

Iam curious I see that boaphilies offers two rows of 4 in heat tape on their ball room rack . And I have read that c serpents will do the same with their 3 in if requested at a extra charge.
Question is why don't they just use the 6 or 11 in an call it good and what purpose does have two rows of heat solve other than more belly heat?

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I assume it's to provide a bigger hot spot and help raise the overall ambient temperature

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not sure but it might have something to do with the wattage or energy effectiveness of shorter heat tape.

Atleast with the heat tape I get, 3 inch is 10watt per foot, 4 inch is 8w and 12 inch is 20w. So 3 inch heats more for the same area.