Devo 7E Throttle output percentage

Hi,
I am tring to configure my Devo 7e throttle curve on Stunt mode.
i set the following points

H - 100%
M - 65%
L - -100%

but when i move the stick to minmum the throttle output appears as 87.5% on the main screen.

( at maximum position it apears as 100% and at middle position 65% )

any idea

Thanks,