Normally I use larger capacity size spinning reels for bass (30 , 35 & 40 size) when using 7lb. to 10lb. FC line for bass (less line coiling) .

Now with a switch to Braid + FC leader I'm thinking the braid coming off in tighter coils (i.e. 20 & 25 size spinning reel) would be better and prevent more tangles from braid hitting the first rod guide in larger coils due to a larger size spool diameter ? ... Also you don't need the larger 30 ~ 40 size reels when <20lb. braid is the same diameter as 4lb. - 6lb. FC ? ... Am I on the right track here ?

I'd say you are. That's been my theory and it seems to work, although I don't have any emperical evidence to support my beliefs :-D

I greatly prefer the smaller size reels due to the way they balance on today's lighter rods.  If the drag is good, no problem.  I don't have any problem with line management using light braid (15lb.) and a fluoro leader.

 

 

Tight lines,

Bob

Braid will perform equally well on either size reel. However, if you want to go to smaller spinning reels you are correct that 10#> line doesn't manage as well on them. 

10lb braid on a 1000 size shimano is my favorite spinning setup. 

In my case the performance is the same with any size reel. Tangles or windknots happen when I throw a lure that's light.  My saltwater reels 3000-4000-7000-8000 have 15 & 20# braid, since I toss near or higher than max rod lure weight I seldom get windknots.  My freshwater reels from 25-30-35 using 10 & 15# braid get knots all the time when using light lures, seldom when a heavier a lure is used. PP, PPslick, Fins, Suffix performance and 832 and several other brands used over the years.  About 6 weeks ago spooled up with 10# US braid not a knot yet, hmm......maybe something to it.  Covering 1 more base, my Shimano and Daiwa reels have never knotted but I'm throwing heavier lures with those reels, but my ul is a trion and no knots using that reel.  Question, is it the reel management or lure weight, this could get interesting.