First off, the instructions right there on the Ryonet site, say nothing about placing the strips underneath, where they will do a more accurate reading. I learned that myself through similar painful trial and error, with an even smaller dryer, an old four foot Ranar Scamp. (I also learned to cut the strips down the center to double my stash.)
As for your experience with two different readings at 35, was the dryer warmed up on the first reading? (I'm guessing 15 minutes at least)
Your little dryer will also be especially susceptible to temperature fluctuation by drafts.
The guns, which run anywhere from $20-$125, can be very helpful, but once again remember that is a surface reading, and a reading of 320 does not mean that the entire ink layer has reached that temp. You will learn a relationship between your reading and the actual ink temp.
I see a momentary reading of about 380 the instant before a shirt exits my tunnel.
In the end, the washing machine is your friend, and the only true test.