Basically, the bottom number of the 80-120 rule goes like this:
Assuming the plan did an H last time, as long as the count stays above 80, the plan can continue to file the H. If it is under 100, it may file an H or I. If the plan goes below 80, it mst file an I.
In this case, I'd do an I. I think the accountant just wants to do the audit to generate fees. Or even just to keep it simple and continue to do an H, this way he (or she) doesn't have to revisit whether or not an audit will be done on the plan year-to-year.