I actually spoke to Rich at Reptile Basics about this yesterday. Flexwatt is made by the same people that make the Zoomed and other pet store type UTH's. It's a printed circuit board type heater and sometimes the ink is thicker in spots. It gets hotter in those spots and cooler in the "thin" areas.

He said you get more consistent temps in a cloth type UTH like his Ultratherm Heat Pads but there will always be variances in the UTH area.

He also said that the temps vary based on the room temp if you don't use a t-stat. It's more of a problem if the room gets too hot because the UTH will get hotter if there's nothing adjusting it.

Hope that helps.
JohnNJ