KO Minus Counts
What you saw is not that unusual. Look at the KO book, p.104 and notice that for 6 decks, for IRC=-20, the Key Count, where you increase your bet, is -4. You don't have to wait for a plus count. By the time RC gets to 0 you should be betting about half your max bet. At this point, on average, the expectation is about .6%. The Pivot Point, where most players make their max bet, is +4 and you won't get there very often in a 6 or 8 deck game.
I prefer to use IRC=0; it's easier to count and things don't seem quite so negative. See Appendix VIII in the book.
Also, KO betting and strategy are based on average values over the shoe. They are right on at the Pivot Point, and good near that point, but the farther you are from the PP the less accurate. You can make more bets above minimum by realizing that, for example, (assuming your IRC=-20), RC=-9 after one deck dealt is as good as the Key Count of -6 based on an average of 3 decks dealt, and justifies an increased bet. Just keep an eye on the discard tray.
Hope this makes some sense.