https://wiki.factorio.com/Quality
Looks like the Quality bonus for equipment grid is fixed - +1 equipment grid size (both dimensions) per quality level
I think there is no way to override it now. If someone know how to specify equipment grid size per quality level, I will add it.
Second option that is possible to do is chage the dimension of all companion equipments from 2x2 to 1x1 and shrink the equipment grid size from 10x2 to 5x1.
The capacity will remain 5 items and growth by one row/column wont be useless