I think MechA 6 is at min, reducing it with only one Arm would mean you can't reach Atoms from the other side, without prebonding them, which is too complicated for me.
Using 2 Arms would mean only 3 Actual Hexes to work with, and one Arm can only pivot.

All  in all Area (and Mech-Area) are my least favourite Metrics for now, but I am all the more excited to see what is actually possibe if you know what you are doing. ^^