I have a 30gal HLT with an e element at the bottom. No thermometer atm. I find that when I check the temp at the top, it varies about a degree across the surface, maybe a little less. Say I found it to be 177degF-ish. I then stir well, and measure 173-174. Stratification is occurring. I would put the probe in the middle, and do some experiments with stirring. It's easy enough to do.