John;
I've been thinking about the same things pertaining to my San Juan 21, which is in a slip so slugs make more sense, seeing as how the sail stays on the boat. I'm going out Saturday and putting them on the sail.
Here's what Sailrite advises about slugs near the tack:
"It is a good idea not to put a slide or slug within 30 inches or so of the tack. This is especially the case if the sail will be reefed since any hardware below the luff cringle will either have to be removed from the track or slot or the reef at the tack will have to be stacked above the stop in the track or slot. Indeed, this is a good reason for not installing any slides or slugs below the first reef cringle."
This makes sense to me, and I'm going to leave slugs off the lower part of the sail, then hoist it and go sailing and see if that matters.
Full page of ideas at:
http://www.sailrite.com/Installation-of-Slugs-or-Slides
Carlos