SUMIFS with Array Constant Fails

Hello folks, many hours trying to figure what I am missing. Notice in the formula below that one of the SUMIFS criteria is an array constant {"MCH","IGT","STT"}

=SUM(SUMIFS(tData[Amount],tData[Plant],{"MCH","IGT","STT"},tData[Category],"Budget",tData[Date],X$7))

That works fine. However, assume the array constant is elsewhere in a cell named 'fPlants'. I cannot figure out why the formula below will not work - it sums to zero which is incorrect

=SUM(SUMIFS(tData[Amount],tData[Plant],fPlants,tData[Category],"Budget",tData[Date],X$7))

If I step through the formula using Evaluate Formula, notice below that there are extra quotes added to the array constant

Formula.jpg

What am I doing wrong? Any advise would be appreciated