Heat for tubs

Hi can anyone tell me whats happening.Im a bit confused.I got myself a digital thermometer with probe.When I put the probe in the tub on the hot spot.The temp reads 77.4.The thing thats confusing me is, If I put a thin sheet of tissue over the probe the temp goes up to the temp I need.If I take the tissue of the probe in the tub,the temp goes down again.Now ive put a sheet of news paper on the floor of the plastic tub.I put the probe of the thermometer on the sheet of news paper.Left the tissue of the probe and my reading is starting and staying at 85.1.

The sheet of paper over the probe traps the heat, hence it gets hotter. For example, in my tank I have 2 thermometers. One reads the ambient temp and humidity on the cooler side (where my bp stays most of the time) and the other is for the warmer side. When I put the other's probe in the cooler ends hide, it always reads few degrees higher. (IE. ambient reads 81, the probe in the hide reads 83.5)

You should just put the probe on the newspaper, and crank up the UTHs a bit, until the thermometer reads 81-84