As there is no reference point on the booms for the elevators I kinda scratched my head about this set up too. It's important to follow the instructions precisely with the rod length and to set the servo horns up so that neutral is exactly 90 Dev to the mounting plate. Once you do that you have a good reference point for the elevator neutral and can trim from there.

I scanned a copy of my my manual. It's an older version but send me a pm and I'll email it to you.

PaulD