This all depends on your contracted rate, or your rate code with AVIS.

Not all rates have a "drop charge". For me, one-way rentals are charged at a rate plus 40 cents a mile, while roundtrips are just the rate.

Find out what your corporate rate is, and then you can figure out the differences.

Regardless, you can always fix things with AVIS Customer Service after the fact - you dont necessarily need the counter to fix things (although it may be more comforting to do so).