This happens to me as well.
I open the ballast valve before driving the boat onto the trailer. I winch it up tight and then go up the ramp far enough for the ballast to drain. The boat shifts though, leaving a gap of about 3 inches. Then I snug up the winch strap again, reducing the gap a lot. But don't be fooled. You're not moving the boat, you're bending the tongue/ladder up and back towards the bow to get the roller to touch. Then I close the ballast value and back the boat into the water to float it again. Then I snug up the winch strap and pull it up the ramp again. I sometimes repeat this more than once to finally get the boat all the way forward, but even then I probably still have some bend in the tongue.
If you don't believe the tongue is bending up, then simply loosen the trap on level ground and see the gap increase. Obviously the boat is not sliding backwards! If the bow is touching the roller and you loosen the strap and it's still touching, then it really is all the way forward.
The brake/bump doesn't seem to work for me, possibly because my boat has old bottom paint on it making it rough. ISomebody here suggested squirting liquid dish soap on the bunks before retrieving. I suppose this might help a clean hull to slide, and/or making it easier to push off the bunks next time you launch. I remember wondering if the lubrication would make it dangerous driving down the highway?
I had to retrieve my boat at the beginning of August. I left the 3" gap thinking that I'd be re-launching again in a few weeks, but it will stay on the trailer until next summer now. I would never trailer it far like this but it's less than 1/2 mile from the ramp to my driveway, on a level private road in a resort/trailer park. With the large gap and the trailer detached on my driveway, when I step on the swim ladder to climb aboard the jack stand lifts up and the back of the trailer hits the ground. And I only weight 150 lbs. Clearly you don't want to tow it like this! I put a block of wood under the back of the trailer so I can climb up. This was the first time in 18 years that I've left a large gap.
Another trick I do is to help center the boat on the trailer. I have those goal-post-like trailer guides on the trailer. When I first drive the boat onto the trailer, I put bungee cords around those posts and the stern rail seat bars, with the same number of wraps on each side to snug the posts and boat. When I pull up the ramp, it settles right in the middle every time. I worried that an inch or two off center was putting more weight on the wheel and bearing on one side of the trailer, and the single-axle trailer is badly inadequate already.