STI wing builders ?

[Kitfox Pilot]

At 6:34 of this video , https://www.youtube.com/watch?v=v5wfnI-HK9A , Brandon is cutting the filler rib. I'm ready to install these and find no where in my book it talks about cutting the filler ribs. Am I missing it or is this for something special?
Thanks for any info.

[SomeDay7]

It’s just some extra wood you can loose and it opens up that space. I cut mine slightly different.

[Kitfox Pilot]

I was just making sure there wasn't something coming up later that needed a cutout. Thanks