So I'm trying to construct a balanced defence range when we open in MP to 3bb and get 3bet by the CO to 9bb.

Say we open a standard MP range of roughly 206 combos and our MDF in this situation is approx 45% (could be wrong) this means we should defend roughly 90 combos.

How the hell do we build a balanced defence range including 4bet call, 4bet fold and flatting sub ranges with only 90 combos?

I work out that we need a bluff:value ratio of 3:1 since when V shoves (100bbs effective) our MDF= 25% (again my math could be completely wrong here).

If my math is correct here I just don't understand how we can build a complete range with so little combos, the range I have built is:

4bet/stack off: AA, KK (12 combos) 4bet/fold: KQo, KQs, AJs, A2-A5s (36 combos) flat: AQo, AKo, AKs, AQs, QQ, JJ (44 combos)

This gives a total of 92 combos which seems fine according to my maths but feels so nitty. Any help would be appreciated