The location of <aiin> and <ain> groups

[nickpelling]

If this is correct for all lines (not just paragraph-initial and page-initial lines), then it strongly suggests that (a) it is not the first word in a line that gets shortened into some second word by having some putative prefix removed and/or by autocopying, but instead (b) that the first word is typically longer than all the other words because an entirely separate process is going on there, one that prepends an extra letter to the first word of each line.

It doesn't have to be every line, though, does it? Even every other line having an added character would up the average.

For sure: or it could just as well be some pages rather than others, as opposed to some lines rather than others. But the average 1st / 2nd / 3rd / etc word length on paragraph-initial lines as opposed to the average 1st / 2nd / 3rd / etc word length on non-paragraph-initial lines is a fairly straightforward and theory-neutral statistic to work out, if you discard label and zodiac pages etc.