Reference to a column total of table calculation

I have two custom measures inside pivot that I sum up by creating table calculations.

Let’s call those measures MA and MB, and the result of the sum is called SumAB

I enabled totals and I get all totals like below:

Just wanted to confirm background is green so it’s table calculations. Now I have each total across a pivot so I want simple calculation pivot change. I create new table calculations but the only references I see are:

${ma:total}

${mb:total}

but I can’t see ${sumab:total}. I tested it by inserting this as new table calculation but I get an error that the field is not in current query