Could "a" be a ligature?

[Bluetoes101]

Ah I see. There's a couple of fringe cases.
(just using Voynichese site so.. pinch of salt)

o - 21895
on - 5
oin - 26
oiin - 196
oiiin - 38
oiiiin - 1

a - 13614 
an - 126
ain - 1717
aiin - 3861
aiiin - 111
aiiiin - 0

So you could make a pretty good guess until your most unsure stage "Xiiin", if that implies anything or not I don't know.