I've read a book that proposes the Uston Advanced Plus/Minus system (tags +1 for 3,4,5,6,7, -1 for X,J,Q;K,A and 0 for 2,8,9) where true count is calculated using full decks and has this strange betting system for 6 decks:
1 deck gone, raise your bet when TC=+4
3 decks gone, raise your bet...