This is probably pretty minor, but by raising the boom you are also effectively raising the center of effort of the sail. I'm sure the depth of your reef is greater than 18", so the rise in CE is probably pretty close to neutral, but it will still be higher than if you didn't raise the boom. A higher CE will mean what sail is left will have somewhat greater heeling force. Not something you'll likely need to worry about in one-reef weather.

Another point with the sliding gooseneck is it takes much less force to tauten the luff. Many boats which use it do not have the winch power necessary to flatten the mainsail for heavy weather without it. Similar to the Cuningham, the "first reef" as the wind blows up is a quick pull on the downhaul to flatten the sail and draw the draft forward. And any subsequent reef will likewise be hauled taut pulling down on the boom. I wouldn't be in a hurry to get rid of it, but go ahead and develop other techniques of maximizing its usefulness.