Bye thee waye:

I have to process RowHeights separately from MergeCells, so I have two
approaches.

First, I determine the Areas for each row that will contain merge cells.
Each such row will have up to, currently, 4 such areas.
I then do the RowHeight adjustment,

I then have 2 choices on WHEN to do the MergeCells.

1. I can do it row by row just after I adjust rowheight. This has the
advantage of eliminating the area string length issue,
but requires extra merge operations.

2. Create an area string that has all the cells to be merged and do the
merge in one operation. This should be faster
than doing separate merges, but requires me to address the length of the
area string