winch height
The winch strap should be level with the bow eye or slightly above when the boat is in it’s final resting place on the trailer.
Think of the trailer on the angled launch ramp and the boat is floating level on the water above it, the stern is not touching the rear set of trailer rollers. That last two feet you’re winching the boat forward may look like you’re lifting the bow, but you’re pulling it down and lifting the stern further away from the rear rollers. When you pull the trailer up the ramp the stern settles down on the rear rollers thus adding additional pressure on the front rollers and bow eye. This is when the bow will actually lift away from the bow chock when pulled out of the water, when this happens owners talk about a second winch or come-a-long, soaping the bunks or slamming the brakes on in the parking lot to slide the boat forward.
If the winch is level or slightly above the eye you’ll be lifting the bow up and sinking the stern and starting to mirror the trailer on the angled launch ramp.
Winching the boat onto the trailer with rollers is fine, a trailer with bunks winching creates way too much stress on the bow eye because of the friction the bunks make, that is why boats have to be floated on to bunk type trailers.