The ULT shims affect the "timing" of the mag and shouldn't affect the trigger rod length. The shims in the ULT push to on-off top and therefore the top oring farther away from the rest of the assembly. This means the pin doesn't have to travel as far to open and release air into the front chamber. It is critical to make sure the sear is rotated far enough forward to catch the bolt before the on-off pin clears the sealing edge of the top oring in the on-off assembly. Thus, it is essential that you don't install too many shims in the ULT or the on-off will open too soon and cause air entering the chamber to halt the reset action of the bolt. It can also cause the bolt to shoot forward again causing a full auto action if enough air gets in fast enough.
The sear in its fully reset forward position is not affected by the location of the top section and is only fully reset when it rests against the bolt spring or a stopper in the rail. You adjust the length of the trigger rod to allow the trigger to move the sear within this range. When the sear is fully rotated forward, hold the trigger against the safety and adjust the trigger rod so that is almost hits the back of the trigger. This will ensure that the sear can always rotate forward to allow a proper unimpeded reset. Yes, the sear will allow the on-off to open before that, but you don't want to limit the forward movement or you will limit the life expectancy of your sear and bolt.
Except for the Automag in front, its usually the man behind the equipment that counts.