I don't have any agreement about this sequence but I always play that when they intervene our NT (or we bid NT over their opening bid) the level of 4 remains the same: 4♣ choose a Major, 4♦ heart xfer, 4♥ spade xfer, 4♠ asks for the number of aces, 4NT quantitative. But in this case I don't have any agreement I guess in the case of diamonds (when they opened hearts) it sounds better as natural to play and in the second case I like Ken's option (asking for how good the stopper is).