IST, consider a BTS:
3 sectors, all synchronized.
1×1 –> all sectors use same freuency
same HSN + different MAIO –> each cell will NEVER use the same frequency as its 2 neighbors.
Excellent choice, isn’t it ?
Now, for 1×3 (with non adjacent freq among the 3 MA lists) or different HSN, then you’re right, the MAIO doesn’t change anything.