If your ramp is perfectly level that roller for the keel will work. If your ramp has a slope to it, the keel will float above it till you pull the trailer out of the water.
Remove roller and mount up near the bow to help lift the bow out of the water and sink the stern, so the hull is closer to the angle of the trailer on the ramp.
When you pull the boat and trailer out of the water. The stern, floating high above the back end of the trailer bunks will come down and lift the bow up and away from the trailer winch. This is when guys will use the brake and slide idea to move the hull forward on the trailer. By lifting the bow up to the winch with the use of a bow roller on your trailer, you will eliminate most of this lift.
The photo with the roller is my boat, and the roller is locater 1/3 of the distance from the winch to the front end of the trailer bunks. Notice the gap between the roller and the hull, this is the extra lift the bow gets when the stern sits down on the rear end of the trailer bunks. It also, lifts the hull up over the front ends of the trailer bunks reducing the friction and the stress on the hull’s bow eye.
Another photo shows a trailer with a small ramp and a roller to accomplish the same idea.
The third photo shows the keel guides up next to the hull, which is the best location for them, after experiencing 30 years of launching and recovering sailboats.