This is a common problem, not specific to box sets. (Also, I’m not sure you’re using “work” in the way that we understand works in MusicBrainz terminology, do you mean recordings maybe?)
You may want to look into solutions proposed in threads like these to get the desired behaviour (from Picard at least):
Those are not really equivalent at all. You can buy a single boxset containing 15 albums or you can buy those 15 albums individually, they’d still arrive in an (additional) brown Amazon box, but they’d be 1 single item vs. 15 separate items in Amazon’s storefront, which is the data we’re mirroring here: 1 single item (1 release in 1 release-group) vs. 15 separate items (15 releases in 15 different release-groups).