90.1 specifies part load values using SEER, which is really just a BS number. SEER can only be determined "after the fact" and most programs use unloading curves instead.
There are an infinite number of unloading curves that essentially yield the same SEER (depending on the weather), so, one could "fudge" the unloading curve to use more energy in the baseline and would still be within the constraints of 90.1/LEED
