Sun Cat performance which MAY apply to your Horizon Cat.
When sailing to weather SOLO in 15-20 knots of wind (with higher gusts) I've found that REEFING the main'sl is an absolute must in order to keep the boat on her feet, avoid rudder stall, and uncontrolled rounding up. However, with another person or two aboard to serve as additional ballast or "rail meat" on the high side, you can sail effectively and comfortably with the FULL Main'sl. Of course, increasing luff and foot tension to achieve a flatter sail shape also helps. By the way, the gaff on the Sun Cat is normally set at a high angle, almost high enough to be mistaken for a Gunter Rig at distance. Adjusting the Peak Halyard tension will also affect sail shape.
And, you will read and hear that the Catboat boom should NEVER be brought any closer to the centerline than the stern cleats, aft quarter, or thereabouts.
Hope this helps.