Thermometer probe position?

[jphealy]

Where exactly do I position the probe from the thermometer on the warm side? Is it about an inch or so above the substrate (just kitchen towels for the moment) or actually sitting on the substrate? I ask because I'm worried that there may be too much belly heat directly on the surface above the UTH. The temp an inch or so above it is perfect, however.

[rex322]

i put mine right on the substrate