Well, one problem is that the harmonics are in a different place depending on whether the string is in flat, natural, or sharp, since the disc changes the speaking length of the string.
I carry a sharpie marker in my string bag for marking the location of harmonics on the string, the more exposed/solo they are the more dots you will see on the strings which generally wear off on their own in a couple of days. I find the placement varies wildly (in my opinion) from harp to harp – where I am used to playing the harmonic on my own harp at home will be completely different for the same harmonic on the symphony’s harp!