> not only are the glasses typically much smaller (this is fine) but they also leave massive gaps at the top

I'm wondering if this is due to the prevalence of cask ales vs bottle/keg conditioning. The former is relatively uncommon in Belgium and you want the head from the latter.

That said, oversized glassware (e.g. Duvel's tulip for aromatics) and/or fill lines are also used to accommodate the head while still not cheating the customer out of volume.