I have 2 tubs, 1 with newspaper and 1 with sanichips in the same rack. When i use a tempgun on the newspaper, I get a significantly lower reading than i do with the sanichips. I figure this is for 1 of 2 reasons

1. the newspaper is slightly raised or curled above the surface of the tub, creating a cooler air pocket.

or

2. The tub filled with sanichips is holding heat better than than newspaper, even though the 1 inch of chips keeps the snake further from the heat source.

Does substrate make that much of a difference?

Also, when using a thermometer with a probe, should that probe be on top of newspaper or under it when measuring the basking spot?