The origin of the base shapes of the Voynich alphabet

[Anton]

I was thinking about the Voynich alphabet the other day at some interesting angle. Let's say the Voynich alphabet is a constructed alphabet. In other words, it's not taken from any script existing apriori, but rather invented by the guy(s) behind the Voynich. (This may be the case irrespectively of whether it conveys a cipher, an artificial language or even a natural language).

Now, it is often noted that many Voynich symbols resemble medieval Latin abbreviations. However, the abbreviations were quite various, while great part of the Voynich alphabet revolves around the "base shape + modifier (mostly tail modifier, but not exclusively)" scheme, where the two predominant base shapes are e and i, - as also already noted (by Cham and those before him). Let's suppose this is the real principle of construction, and not mere visibilty. That the guy indeed "constructed" characters by combining e and i shapes with modifiers. And, btw, a is e plus i.

Then the question emerges - why these two shapes, in particular? Have they had any special significance anywhere else - whether textually, graphically or semiotically? Where could they have been "borrowed" from, and why?