IMO, whatever the holding for Responder at IMP's, his decision to invite, not-invite, or blast should be the same as at Matchpoints. He makes the straight value-based call, and the person being invited is the one who takes form of scoring into account.
If both partners are taking the form of scoring into account, there seems to be too many 5-7 Imp donations. When the other team has done the same thing, a push at minus is still a 5-7 Imp opportunity cost.