If you do that you are putting the grade before the IDT, when it should be after it.
If your material is LogC, for example, the difference caused by the incorrect order of operations may not be huge, but it’s still wrong and may account for what you are seeing. If you look at the graph where I plotted ACEScc, ACEScct and LogC on the same axes in this Mixing Light article, you will see that ACEScct is not a million miles from LogC.
But order of operations is very important. Not quite right is still wrong!