It is not a spacer for the legs to butt against. It is, in fact, a low angle adapter.
This is how it is intended to be used: Remove the low angle adapter from the bottom of the center column. Remove the center column from the tripod. Invert the low angle adapter and slip it into the top of the tripod where the center column was. Tighten it down with the same knob used to tighten the center column. Mount a tripod head on the 3/8 inch stud protruding from the low angle adapter. You now have a quite solid support that will allow you to use your tripod at a very low angle. With the center column removed and the adapter in place, you can now splay the legs out to 43, 73, or 90 degrees (flat on the ground) if you like.
I did it many times with my 3001 for macro work before I gave the tripod to one of my kids.