Interesting issue here, excel actual struggles with it in a way itself. Say you have a column of data and each row is three merged cells. You only input a single value in each merged cell but excelpython creates a tuple as so:
((Value, None, None), (Value, None, None),.......)

Excel has a similar problem. For example, when using VLOOKUP with merged columns it treats the merged columns as individual cells.

I should add that for a single merged cell excelpython acts as expected.

Having said that, I'm not sure there is a good way to solve this since it is more of an issue of how excel defines a range when selected with a mouse. ie. rows 1 thru 5 when A thru C are merged ends up A1:C5 rather than A1:C1