With a Futaba radio (steering side), EPA is to set the travel of the servo at maximum lock, Dual Rate is then used to set how much lock you want on the track (anything up to 100%).
This seems like the logical way to do it, but from looking at some Sanwa manuals recently they seem to suggest doing it the opposite way! Which means you could have dual rate percentages in excess of 100%
The old KO Esprit had yet another different way of doing it.
Throttle side of an electric car shouldn't need any adjustments to EPA as the ESC will be set up with EPA at 100%. Futaba radios have an ATL adjustment which is basically a dual-rate for the brake side.
I think the best advice is to follow the manual for your radio...