If you're using a Hitec Optic 6 radio, you are probably using the Hitec servos too.

Use one of the adjustable length servo arms that comes with each servo and make the servo arm shorter.

Do this before you change the End Points in the transmitter.

Shorter servo arm = less pushrod throw distance which is what you need here.

It's all there in the manual for the radio system.

You did read the manual, didn't you?