I find I can drag the tuplet number with the mouse up or down with no problems, but when I use the numbers in the properties panel, or the arrow keys on the keyboard, no matter which up or down arrow I use, the tuplet number moves in the same direction.
I don’t find that to be true: a positive number for e.g. ‘Start offset Y’ moves the tuplet number up towards the top of the page, while a negative number moves it towards the bottom of the page.
I checked and you’re right. I think I was doing a triplet in cross staff notation, flipping it up and down and angling it to see what looks better. I’ts at that point that the problem I mentioned occurred but I just tested it again and it works fine