Even if you use the factory thick shim? It usually has a pretty good radius on it. And I've used Ratech kits lots of times. In fact, they were one of the first to supply a crush sleeve eliminator spacer but the first one I got was too long so they got a call from me saying how much too long it was. Once the pinion dept was set, there was no way to get even a bit of bearing preload. Having a lathe, it was no sweat fixing the one in my hand so it didn't slow me down but they sent me a new one anyways. It took a couple of weeks so they probably did some checking and fixed the problem but at least they did it. Some companies just ignore ya.
Rarely do I get a rear end setup that goes 100% smoothly lol so charging by the hour doesn't make sense so charging by the job is more in line. The worse one took me 8 hours to set up! Thought maybe there was a thick shim that wasn't flat or a bearing face fit that had a burr or even a bearing that wasn't right. Man, chased my tail on that one. Finally got it right but never did find anything that was the culprit....