No matter how many cards you have left in the deck, if you clear the table, you get 20k.

How about an extra 500 sP - 1k per card in the deck?

Support--it's a luck/chance game, so I think having a little bit of a bonus per leftover card would make sense. That, and I play Caliph's Tomb obsessively so I'd happily enjoy a higher payout. :P