I don't rely on your method. I put the trike in one of the middle gears on the rear cluster. I kneel behind the trike and adjust the RD barrel adjuster until the lower jockey wheel lines up with the cluster teeth. Hop on the trike and take off to see how it shifts gears. I can get it right on the first try most times. I have a bike stand (like a trainer) discarded by a neighbor but it is more trouble to put it on the stand than it is worth.