Thank you for your hints.
This doesn't influence the dimension of space. Well, it does, but it is a side effect of alignment and line breaking algorithm. One cannot change the space to a particular value/factor.
This would work if the parameter could be dimension (\setupspacing[5pt]), but it cannot.
3. A third factor might be the need to tweak things a bit once
you take a look at what is produced, and where you might need to
use a couple of other options, be it \, \nospace, \thinspace....
If one will finetune every space in the paragraph, this could be a way, but it's far from a nice solution.
\setuplanguage[en][spacing=packed].
This latter especially because I want to avoid some rather ugly
spaces after a period.
Which is an equivalent of \frenchspacing primitive (only regular space after period). In most languages spacing=packed is likely the default setting.
Not at all sure if all the above is what the purists would do,
but from a practical point of view it works for me.
Purists wouldn't change kerning at all, because the font designer knows best, what kerning should be used. Anyway, once the graphic designer starts changing leterspacing (kerning), the space correction is sometimes needed, too. ConTeXt changes the space proportionally to \setupcharacterkerning, which is fine in most cases.
For this use case (short text in one font) primitive \spaceskip3.2pt will do the job
(ragged text thus no glue). I was searching for the more abstract solution like \setupspacing[factor=1.05], because once in a while the correction is needed. Or font goodies could be the way to change spacing.
Regards,
Jano