To the OP, your installer is correct...more or less. Although I do use a self-powered meter. Too much of a pain to constantly rely on the receiver to power the meter. And as far as your transponder/aim thing. It doesn't matter WHAT transponder you peak on. The installer is going to peak on the signal from the particular satellite. Some transponders are going to have stronger signals than others. Admittedly, a 59 on the 129 is pretty weak. But as Scott said, Dish is going to be boosting some of the weaker transponders to hopefully help things.
"You know, Smithers, 'I told you so' has a brother, and his name is 'Shut the hell up!'" -- Monty Burns