when you start geting into 45 degree throws I'm guessing for 3-d use your going to loose serve res. it's simply how it works. You can adjust your throws by adjust what hole the clevis is hooked to. I can't say I ever given any though to calcualting the horn length. just play with it. remember the further the clevis is from the servo the more the surface moves. the closer to the servo the lees the control suface moves. at the control surface the colser to the control surface the more the surface moves. the farther away from the the control surfae the less the surface will move. the one to ratio is a good rule of thumb for percise control. when trying to set up for 3-d your going to get persise control, you set your low rate for percise control. don't go over 110% on the AtV. the problem with ATVs is most if not all Tx don't evenly distribut the stick movement to servo movment when the ATV is moved. so keep it around 95-105 %, personally the only control I use ATV's for is throttle and flaps where you need a persise stop point. If you look really close at what the servo is doing it will almost look like you put expo into the program when the ATV is moved to an extream. on this kind of set up it is a good idea to set in some expo so you little movment near center and alot of movment toward the extream of the stick imput
with a 3-d set up your going to end up setting 30%-50 % for the low rates since your normal deflection is 10-20 degrees. 35 degree plus is for 3-d set ups. 80% low rate would be a normal hi-lo rate for a sport model


my 2 cents