Did you try 'F+' or 'R'?

You should also have a look at the registration of other statistical functions in fpsfunc, RegisterStdBuiltins, e.g.

AddFunction(cat, 'COUNTBLANK','I', 'R', INT_EXCEL_SHEET_FUNC_COUNTBLANK, @fpsCOUNTBLANK);

AddFunction(cat, 'MAX', 'F', 'F+', INT_EXCEL_SHEET_FUNC_MAX, @fpsMAX);

I notice that this part is not very well-documented. I should spend some time on it.

There's one thing I should note here: the formula registration of fpspreadsheet does not work for "array formulas", which are not supported at all. But I think MATCH is not one of them.

P.S.

If you would like to share your code I'd be happy to include MATCH in fpspreadsheet.