sh_ and ch_ compose the same words

[Torsten]

You discussed Voynichese words containing both ch  and sh, true: but there you also asserted that ch and sh are constrained by the shape of the characters next to them. 
I find this hard to understand, given that ch and sh have such a strong affinity for being followed by e and ee, yet have such a strong phobia for being followed by sh and ch.

I'm therefore not sure I can accept this kind of shape-driven argument when ch and ee have such similar shapes.

With the exception of 'i' and 'e' the same glyphs occur rarely repeated. So it comes as no surprise that 'words' like <chchy> or <shshy> are rare.