Well, consider the case where you dont have a GV1 but you do plan
on using cyclic->thr. mixes but dont have a 9Z so your Tx will overthrow
the throttle servo when at max throttle and you give it some cyclic.

The common solution is to max out the subtrim on the throttle servo
so thhe servo cannot move anymore. Then set the servo arm and the
throttle arm so that they are at about 45 degrees (I've noticed most
carbs are actually +/- 42-43), the high ATV to 100 and the rod the
right length. The midpoint will fall to 90 degrees (a Good Thing). However,
when it comes down to low throttle (cut), you will need less than 100 ATV.
Usually, about 80-85. My statement is "So what". The only time I use the
low side is starting and spooling up. In any flight mode, I'm only interested
in the high side.

The important thing is to look at the angles involved and if you have
equal throws on both sides of 90 degrees, you can play w/ the arm lengths
as you desire. You can have a parallelogram or a trapezoid, it doesn't
really matter but each will give a different feel but the setup is mechanically
true.

When you use unequal arm length, you get a multiplication effect which is
OK (note how most mfgrs use different effective arm lengths when doing pushpull). When the arms aren't parallel to each other, you get mechanical offset (due to the sine/cosine of the difference in arm angle).
which is a Bad Thing.