ok, I'll add a few things

1- You will 'lose' some temperature on the glass, but you'll lose even more thru the substrate... (Be prepared to set the temperature anywhere from 5 to 12 degrees higher than what you really want/need)

2- Wooden substrates (aspen, coco, yadda yadda yadda) will take longer to heat than paper towel or newspaper, meaning that the real hotspot SURFACE temperature won't reflect accurately until a few hours

3- As LGray23 Already mentioned 1.5" of substrate is kinda way too much (and it will give you even more trouble getting the right temp inside). Regularly .5" or 1" is ideal.

4- I have been kinda flamed here before for this, but I really don't like setting the T-stat probe in-between the glass and the UTH because of 2 reasons:
(1) The temperature that the T-stat is reading is the actual UTH temp, instead of the
Temperature after it has dispersed through the glass.
(2) Placing the probe between the glass and the UTH will most likely create an air bubble around the probe, meaning less UTH/Glass contact area.


But that's just me