Yes, slat spacing is 3/8 between slats. I understand Brians methodology and should work well with strong hives, but I prefer to keep my SBB's. What will work well in colder climates, will not always work in Fl. and vice versa.
I also would check for the queen under the hive, just not at night. When I changed to SBB's and slatrack's on two of my hives, one took about three days to stop going under it and one never did go under it. I am talking about a significant number of bees, not a handful.
If there is not a queen under it causing the problem, get the bees off of it and block it off until they learn where to enter.