The dual rate option and end point adjustment do provide some overlap of capability. They both effect how much the servo moves for a full stick deflection. Generally, people use EPA to limit the servo travel to avoid binding of the linkage. Then dual rate is used to reduce sensitivity from the maximum. Doing it this way is more important when you have mixes where one stick effects multiple channels.

If you max out both the EPA and dual rate, it's possible you could drive the servo past it's design limit. Also, because the servo output is rotary, you don't get much additional pushrod movement by increasing EPA beyound 100%.

Tom