Why not positional variation?

[Torsten]

Indeed, the shape of a glyph must be compatible with the shape of the previous one, and is also influenced by its position within a word or a line. Currier wrote: "There seem to be very strong constraints in combinations of symbols; only a very limited number of letters occur with each other in certain positions of a 'word'" (see You are not allowed to view links. Register or Login to view.). Following Currier, the glyphs used to write the VMS are mostly based on a curve or on a line as first quill stroke: "We have the fact that you can make up almost any of the other letters out of these two symbols [i] and [e]." (Currier 1976). The glyphs [e], [y], [g], and [s] are based on a curve-stroke, and the glyphs [i], [l], [m], and [r] are their counterparts based on an a line-stroke. The glyph [a] is a combination of a curve and a line stroke ([a] = [e] +[i]). 

Furthermore, Schwerdtfeger has described in 2008 the following four design rules for the VMS (see You are not allowed to view links. Register or Login to view. and You are not allowed to view links. Register or Login to view.): 
(1) line-glyphs can follow line-glyphs or [a]; 
(2) curve-glyphs and [a] can follow curve-glyphs; 
(3) the [l]-glyph can be used as a curve-glyph or as a line-glyph; and 
(4) gallows glyphs count as curve glyphs.

An example of this behaviour is the sequence [che]. The ligature [ch] consists of two [e]-glyphs connected by a dash. [ch] is obviously similar to [sh]. The common Voynich word [chol] therefore can be seen as the combination of a ligature <ch> and a ligature <ol>. Consequently, obvious transformations would be [ch] into [sh], [ol] into [al], [or], and [ar]. Therefore, [chol] could be the origin of words like [shol], [shal], [shor], [shar], [chor], [char], and [chal]. At the same time [ch] is a sequence of two [e]-glyphs. And since [e] can appear repeatedly, it is also possible to add an additional [e]-glyph after [ch], leading to words like [cheol] and [sheol] (see You are not allowed to view links. Register or Login to view.).