Interchangeable ch/sh and k/t characters

[MarcoP]

[Edit:  Getting back on topic here, what I find interesting is how different /sh/ and /ch/ can behave while being so similar.  Despite making similar words like shedy, chedy, sheey, cheey, etc, they definitely have their own "personality" in the manuscript.  /sh/ in particular appears much more in the Top Row of paragraphs than you would expect from its performance in lower lines.  Meanwhile /ch/ tends to go from being a common initial and a rarer word-middle to being a rarer initial and a common word-middle, forming words such as opchey.]

Thank you, Tavie, that’s an excellent point!

In the You are not allowed to view links. Register or Login to view. I linked above, I compared word contacts for chedy/shedy and they appear to overlap so well that I would say there is no clear difference: they have the same adjacent words, with the possible exception of 'daiin'. For comparison, I included data for qokeedy, which is visibly different (e.g. ol.chedy ol.shedy are both frequent, while ol.qokeedy isn’t).
   
Since we don’t have much Voynichese text, word stats are only possible for very frequent words, but from that experiment I get the impression that the system fails to clearly differentiate ch from sh.

A few years later, Patrick Feaster published results that describe the behavior you mentioned (You are not allowed to view links. Register or Login to view., 2022). He developed a simple and effective way to present glyph distribution in paragraphs, mapping all paragraphs to a square shape where the first line of paragraphs contributes to the top row of the square and the last line of paragraphs contributes to the bottom row (similarly, columns correspond to different left-right positions in lines, with the first and last column corresponding to first and last word in a line respectively).

Patrick included images for both sh-(blue) vs ch-(red), and k(blue) vs t(red). Stats for sh- and ch- are limited to word-start positions. 
This is part of his figure 3: “Rightward and downward distribution of words beginning [Sh] in blue and words beginning [ch] in red (left); words containing [k] in blue and words containing [t] in red” (right).
   
One can easily see that, as you say, sh- dominates the first first line of paragraphs. The black column on the left is due to the well-known properties of the first word in lines, where peculiar word-types are produced by the apparent prefixing of characters like d- and gallows, so that line-initial benches are almost entirely absent; this equally affects ch- and sh-.
Pink - word-initial bench; green - bench elsewhere:
   

For k/t, the divide has a diagonal shape: k prefers the bottom-left, t the top-right; in this case the first column is markedly different, with a purple color showing a similar frequency for both glyphs.

In principle, one could think that the vertical preferences of sh- and ch- could correspond to semantic features, like some sh- words being frequent at the start of paragraphs, but if the difference was semantic we would see marked differences in word contacts for sh- and ch-words, and we don’t. Also, sh- markedly prefers the first line only, there is not a gradual vertical decline in its frequency, as I would expect for something due to word meaning.