Didn't know personally... So I got this from the 'net:
I do know that in the past someone told me to wait a while before adding the vinegar..... but that is a distant memory.
1) Did you wait a few minutes after grating? There's an enzyme that reacts with oxygen IIRC, and it should get hotter after a few minutes of rest.
2) You have to get some cell crushing going on to release the chemical that makes the hot flavor, so microplaning may not have done enough cell damage, depending on how sharp your tool was. Also, acid stops the development of the heat. Root veg lasts a very long time, so I recommend going with a box grater to create a pile of root, letting it sit a few minutes, then mixing it into your preferred sauce vehicle when the flavor is developed.
3) The microplane likely isn't doing enough damage to the cells to release the isothiocyanates. A food processor would be the way to go.