Mainsail rigging
I also have a 1981 Macgregor 25. My setup has been modified slightly as I have slab reefing instead of roller reefing, sail slugs to assist the main in the sail track and a cunningham, however these changes do not alter the basics. Basically it is important to be able to control luff tension. This is more important than the actual position of the sail on the mast. (within reason as it should still be reasonably close to the top.)The luff tension can be controlled by.1. halyard tension,2. a cunningham, or 3. a sliding gooseneck with an appropriate downhaul.As the wind freshens greater luff tension is required to assist in flattening the main sail. As my sail is close to the top I cannot acheive this with the halyard so I use a cunningham. Although this does not maximise sail area it does have the advantage of not reducing head clearence to the boom. Many sailors acheive the same thing and maximise the sail area with a sliding gooseneck. By applying downward pressure to the boom and sliding it down the mast with a pulley arrangement they acheive increased luff tension while maximising sail area. Now that you have installed roller reefing which no doubt includes a fixed gooseneck position and if you are unable to increase luff tension as required by using the halyard it may be worth having a cunningham hole placed in the sail and fit the appropriate downhaul which can be controlled from the cockpit. If you retain the sliding goose neck fit a stopper just below the maximum travel of the goosenck to stop it slding down when halyard pressure is released. (My gooseneck is below the sail feed area and I use a pin to stop the sail slugs coming down the track and falling out. I remove the pin when the main is up to avoid anyone injuring themselves on it when we are actually sailing.) A boom vang is a great addition. Along with halyard tension it helps flatten the sail as the wind increases. I recommend fitting a vang, however this is an additional tool to assist in flattening the main not a replacement one.I would solve the problem of luff tension first and then move onto the next challenge. With best regards,Willem