I think you mean start at 4.5
I just finally realised it will work at size 4.5 by using mHill and iGrass
Turn 1 size 4.5 iCow, mGoat, mBG, mGrass -> 8sh + 3 on growth -> 11
Turn 2 size 5.0 iCow, mGoat, mBG, mGrass, mGrass -> 9 sh (20)
Turn 3 size 5.5 iCow, mGoat, mBG, mGrass, mGrass -> 9sh +3 -> 12 (horse)
Turn 4 size 6.0 iCow, MGoat, mBG, mGrass, mGrass, mGrass -> 10 (worker)
Turn 5 size 5.5 iCow, mGoat, mBG, mGrass, mGrass -> 9sh +3 -> 12 (worker)
Turn 6 size 5.0 iCow, mGoat, mBG, mHill, iGrass -> 10sh -> worker
Further MM should remove shield wastage perhaps sharing goats with Ulundi
Edit - this is not to say we should do it, just that we could