The EP500 may simply be inverting the signal on the way in, or your receiver may be inverting and the EP500 not inverting. As far as I know there are only loose conventions (if any) about relationship between cone movement and signal polarity.

The only "hard" rule is "have someone flip the damn switch and see what happens"

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8