Check your PM.
I just followed the manual in setting up the headspeed using the travel adjust. Remember to do the transmitter Quick setup steps before you adjust the ATG. It's easier to setup with a G-view.
My Idle1 was ~1850 or so and my Idle2 was setup for 2010-2100 RPM.
The ATG is very accurate for headspeed settings. Select the correct gear ratio, then using your Travel adjust, look at the Flashing LED's and the order they are flashing to get to your target headspeed.
Go to the link below, then scroll down and click on the product FAQ's on the bottom right. There are some good tips there.http://www.curtisyoungblood.com/products_view.php?id=17
Oh, one more thing to note, on my DX7, to get the ATG to have headspeeds linked with the flight mode switch, you have to make a program mix.
Go to Prog. Mix 1
Set AUX2 -> AUX2
My travel Adjust worked out to be +62% and -114%
This will very depending on how you setup your headspeed.
At least this is a start for you.