And ballast up when they wish for better penetration.

For their cross country events, they usually fill their ballast tanks with water. It's fun to watch them scream through the last gate and pull the plug. They're actually not very dainty either. You can't have that high an aspect ratio wing and it be what you'd call light.

Many years of excellent fun were spent slope soaring R/C gliders. Every one had a way to ballast. I built a series of 2Ms that were excellent thermal soarers and did very, very well on the slopes. They had a ballast box to fit a lead weight I'd cast for the purpose that was about 2x2x4 and was almost what the glider weighed.