I suspect it's the default sorting.
You and I would read this:
Widget Sales Jan Feb Mar
Type A 123 456 789
Type B 543 231 233
"across then down" but Monarch reads MCRs as down then across. If you have a large data set the second column might be a long way down.
Using 10.5 or above you can sort on Column() and Page () and Line() to give you the logical order you want.
Hope this helps,