JSWolf, thanks for your reply.
I agree with you that huge 'reset' or 'normalize' blocks are generally unnecessary, but this little hack seems to be useful to prevent monospaced texts from looking tiny.
In any case, I only place it when
code or another monospace class is actually used in the epub.
BTW, I have continued testing and with the Big Three they look like this:
Apple iBooks (v15)
Kindle (azw3 /Calibre)
Kobo (kepub /kepubify)

(as we know, Kobo doesn't yet have a monospaced font... but it does resize just like other engines. Epub —read by ADE— has no differences.)
I leave it here in case anyone else finds it useful.

Thanks for your attention!