Calendar In Excel Issues

I am using the Phil Johnson calendar in my excel file. I can assign a single cell to pop up with the calendar but I am having issues getting the calendar to work with merged cells. I can put all of the cells into the code but the cell won't open the calendar, as soon as I unmerge the cells each cell works fine. Trying to get it to work with my current layout so I don't have to redesign the file. Has anyone been able to get this to work with a merged cell?

I am not familiar with the Phil Johnson calendar. Is it truly necessary that the cells be merged, or is it possible to assign the value to a single cell and just use formatting to make it visually appear that they're merged (using combination of colored & white borders)?