We are finishing a bedroom and bathroom in the basement.

Here in the front range of Colorado we are required to have floating walls in the basement because the soils tend to heave.

I see that fire or draft blocking is now required. I understand the concept and how to do the top part of the wall and even the vertical blocks. I have just finished putting up the vertical blocks with a combination of 2x4s and 3/4 OSB.

However, how does one take care of the big 2.5" gap at the bottom plate which cannot be anchored to anything. It really seems to defeat the purpose of trying to block the draft when it can just go down the concrete wall, sneak thru the gap at the bottom plate and back up on the other side of the vertical block. Am I over thinking this? Any ideas?