We've had the same problem with our R25. We've destroyed 2 winches so far, before realizing what the problem is. Yes, it has to do with the geometry of the boat and trailer, and the change in angles as it settles. The boat, of course, stays level as it moves from the water to the trailer. The trailer, however, transitions from whatever angle it is at under water, to being level under the boat as it comes up the ramp. The changing angles will cause the roller and winch assembly to move lower and forward in relation to the bow eye, often 6 to 8 inches depending on the steepness of the ramp. If you run the boat right up to the roller and winch the strap tight, you will have the weight of the boat, plus leverage, straining against the strap as the boat settles, and the winch will break.
We now bring the boat up to the roller and hook everything up, but we give it some slack as we slowly work it up the ramp. The idea is to give enough slack not to break things, but hopefully keep the boat from slipping back on the bunks. Once the boat is out, we suck everything tight and do the "Ranger Bump". Then re-tighten everything once you're up to the roller.
I hate doing the "bump". It seems so hard on all the equipment. There must be another way.
Someone mentioned moving the entire winch stand forward 6 inches before retrieving, then bring the boat right up to the roller. Let the boat settle on the trailer with the 6 inch gap as it wants to (right where it is supposed to be), then move the winch stand back again till the roller touches the boat. I might try that next time, It sounds like the least stressful option.