Difference between ambient temperature and dryer plenum temperature is a large driving factor in fuel usage (raw heat required to get to drying temp), as is the moisture of the material being dried (wetter = longer time in the dryer = more time raising temp from ambient to plenum = more fuel burned). Grain quality (air flow), design/efficiency, and ambient humidity are smaller factors.
I work in the natural gas utility industry supplying gas to all types of dryers from in-bin to cross flow to commercial tower and everything in between (Farm Fan, Meyer, GSI, Zimmerman, NECO, Sukup, etc.). Usage differences we observe on our natural gas system are heavily dependent on outdoor temps. In my experience, a quality modern tower dryer drying field corn will use ~65% of it's max burner rating drying corn commercially at 25-30 Deg F ambient with a plenum temp of +/-215 Deg F. If temps are in the 60's or 70's that number drops back to 40-50% max burner capacity......if less than 20 deg F, you see an increase above 65% (don't see that much due to rate structure at my employer financially de-incentivizing drying at temps under 25 deg). I would expect a 7000 BU/hr (5% removal rating) Zimmerman tower dryer (max burner rating of 74MMBtu/hr) to operate around 42 MMBtu/hr at 25-30 deg F once warmed up and full of grain.
For older used dryers and smaller continuous flow dryers the percentage numbers are probably a little higher due to improvements in efficiency in modern tower dryers.
To be clear, I don't operate the dryers, but I have observed their gas usage rates over time (30 years) and on various types, so our system models for predicting usage are pretty dialed in.
BTW, In my experience the "Average fuel usage" number published by the dryer manufacturers is usually around 45-50% of max burner rating and roughly correlated to 60 Deg F ambient temp. Very few manufacturers put a temp with their average usage, so that number has to be taken with a grain of salt and applied to your climate.