Do you mean use the terry as a booster? Sorry - didn't follow that so well... Probably if you use a full flanny flat you wouldn't need the terry. (But I still found the full square flanny flat bulky.)
I use half-square terry flats folded into four as boosters or to stuff pocket nappies for Natalie now and I find them absorbent enough for her atm. (Though I wouldn't use terry o'night, only between feeds.)

I usually change after every feed.