this is my idea to the situation
Put the OTA in the horizontal position, move your base till its at the required angle, then swing your ota into position.
Like this device has been created for, i belive that is just a "ball park" figure. And isn't too much different than using the star hopping method. pick that star then that star use a thumbs width to get it about in the right spot, then hey there ya go. pan around and find it.
If you always use the same method for getting something 9 times out of 10 it will have repeatable proformance, eg, it should hit approximately the same spot if all other variables have been contained.