Hi Cheri. Thank you for your question. This is an interesting example because one of the column headings does indeed require Nemeth, and the row headings are words.
As with any table, there is more than one way to transcribe this. My first priority when setting up a table that will be used in a classroom setting is to have the layout match print as much as possible. The second priority is not to overuse keying or transcriber's notes, since that tends to take the reader's attention away from the table itself.
In this table, the issues are not really the row headings. There are only two contractions in those words, so transcribing them in UEB or in Nemeth doesn't change the spacing issues.
Here is what I would do with this table. Write a transcriber's note that "x" means "Partner 1(x)" and that "y" means "Partner 2(y)". Now all you need to do is switch to Nemeth for the "d-squared" column heading. See BRF example, attached.
I don't know why there is no space between 1 and (x), between 2 and (y). I followed print and I transcribed 1(x) and 2(y) in UEB.