By granting the divorce I’m freeing a 5CP card for the English next turn. Not granting it makes them lose a card play (and slows his advance), asking for a card is beneficial for him (even if it’s a random 5CP card) since it’s at worst a break even in CP and it accelerates his conversion, and most times the card will be significantly under 5CP. Two cards is about break even and thus the best starting discussion point. Of course we can do one card + some other secondary deal, but that will depend on the specifics at the moment of the deal (average value of cards in hand, etc…).
My understanding is that the deal needs to happen during the diplomatic phase, isn’t it so?