This option doesn't seem to be working. Unless I am mis-understanding how it is supposed to work.
I set the value to 100 and I still get merged chests with greater than 100 stack locations.
When set to 10, I still get over 100 total locations, but now I can't make a merged chest larger than 3x3.

Ok. I get it now. The merged chest option is the max value of the width x height of the merged chest, and the inventory size limit is what I need to change to set the maximum number of total stack locations in the merged chest.
I feel so dumb now. And I used to be good at math.