The house style we're working in stipulates en dashes with spaces on either side rather than the longer em without spacing. It's uncommon in the US (and it's a US publisher) but it's their house style, and one of just a few minor deviations from Chicago Manual of Style. However, Calluna Sans's en dash seems so unusually short as to nearly be mistaken for a hyphen. My initial response is that it looks atrocious as stubby substitute for an em, with rivers of space on either side, comparatively. Perhaps Calluna's en was never intended for the styles common in Germany, the UK, etc., that don't favor an em for parenthetical thoughts. Would it be justified and legitimate to customize the en by lengthening it slightly, or is this typographic crime, and how would such a basic customization best be done?
Also, are you sure that the en dash is too short? In my copy of Calluna Sans it is twice as long as a regular hyphen and half as long as an em dash:
Alternativly, you could use the minus – which is a bit wider – as an en dash (they are on the same axis).
There is not a single convention: some designers add spacing to en/em dashes, some do not. You’ll find discussions about this issue here on TypeDrawers.
Scala’s en dash is precisely 500 units wide, half the 1000 units per em, while Calluna’s en dash is slightly above half an em wide (522 units for 1000 UPM), but the dash itself is below half an em at 410 units. Again, some designers prefer the precise mathematical construction, some do not, see other posts on this forum.
The question of whether to substitute all en dashes, not limited to just instances of parenthetical usage, but of course also ranges, page number range references, etc., remained, arose, where the slight space on either end of the en looked preferable as it was originally designed. Opting to use both variants of the en, though unorthodox, seemed the most pleasing choice visually.
Thanks to this forum for prompting the successful exchange with the designer.