I'm a DirecTV subscriber, so I don't know jack about the technical aspects of Dish, but I think you answered your own question, "so they can charge me 85/hr."
I'm sure that the retailer will give a reason about the install being unsupported... that it's not covered against system failure or noncompliance to specs (<gain due to smaller dish).
I'd say fight 'em over this on principal... but it probably isn't worth it, especially since the executive office may concur with you technically, but doesn't appear interested in assisting you.
Do you HAVE TO go through your local retailer to get service?
Can't you order directly through Dish online and circumvent them altogether?
Will they not ship receiver(s) to the Islands, and create an account?
In my experience with DirecTV ('95-'05 through Pegasus, '05-present since DirecTV bought 'em out), I have never dealt with a retailer... in fact, I've installed/aligned every dish and system myself.
Back in the Ku days, this included an upgraded (Slimline-sized) dish to replace the 3LNB Ku DirecTV dish.
I had moved north, and I couldn't peak the Ku signals for (101°110°119°) to the levels where they had been (92-97 instead of 95-100).
After the swap, the readings were 97-100, with more than half of those at 100.
I bring this up because there it's empirical evidence that "bigger is better."... but in my case, wasn't necessary.
While I believe that you have the right to get what you want... you do realize that when your signal goes out due to rain, etc., that you will have opened yourself up to finger-pointing that it's YOUR fault.
Don't expect that any service call, from that retailer or anyone else, is going to be performed gratis... in fact, that's a good question to ask the executive office, if they will setup an independent account... if they will guarantee in writing that they will pay for or reimburse for any future service calls.
I think you already know the answer to that...