i think for moving selections up and down(and for some other transformations about y coordinates) in italic fonts we need consider italic angle in many situations. i suggest define an additional shortcut key to bring italic angle related horizontal correction offset in vertical transformations(like opt key with mouse and shortcut keys for moves and an checkbox/argument in other transformations and filters to toggle consider it).
the math is simple(if I’m not mistaken); new x coordinates comes from:
x = x + y.tan(italic_angle)
(I’m not sure round function apply globally in Glyphs app or we need to put in formulates(?))