It seems that they have fallen on the baseline, while they should be center-aligned (see Unicode charts). Needs careful change since the glyphs for the monograms are used for the trigrams etc.
It seems that the glyphs used in the Unicode charts for the monograms and digrams are also a bit thicker. That may need a bit of investigation to see if it is intentional.
Problem exists in Sans and Mono.
Glyphs don't have to look exactly like in the Unicode charts, but I have no knowledge of this so I don't know what is acceptable or not.