Idea:

This glyph, initiating Tuesday, is written exactly in the same way as those which initiate Thursday and Saturday. That surely is a sign for the reader to try to understand.

I guess that the straight horizontal short side at the top - which also Sunday has - is implying a higher status than the downward sloping corresponding sides in Monday, Wednesday and Friday.

At least that was the situation in the Roman circus (cfr Euripus in Hamlet's Mill), where the altars of Moon, Mercury and Venus were at a lower level than the rest of the altars.