Here are the distances I spaced the slugs on my X. This enabled me to reef the stock main without removing the slug stop and with no jackline.
(Taken from my post 5 years ago.)
Starting at the bottom of the sail (foot), measure 0 at the outside bottom of that shiny ring in the corner of the sail (tack). My slugs are placed at 11", 30", 47", 65", (reef point--that other shiny ring part way up the sail next to the pole (mast)--no slug here), and 98". The remainder of the slugs are not relevant--space them as you see fit. I used a total of 14 slugs. The boltrope needs to be taut when measuring.
Using the stop, I could only get enough room to stack 4 slugs during a reef. The placement of the 4th and 5th slug is important to give adequate slack to reef. I needed 33 inches between #4 and #5 slug. It does take a little effort to hook, but it doesn't fall off while you're pulling on that rope attached to the top of the sail (halyard).
If you use my #s, double check to make sure it will work for you. I used the cheap slugs from Sailrite (I think). The ones that screw in. All I can say is it works for me. I have reefed this sail in the dark with the boat pitching (20+ winds, 50 miles offshore). A lot easier not having to worry about losing the stop or a jackline getting in the way.
Maybe this will help. Good Luck.