You're moving the numbers in the wrong direction.
The kill/tag percentages are a juggling act to make sure you get as much spam as possible without getting false positives, I have my kill/tag set at 66/25 respectively - try yours at that and see if there's an improvement. Reducing the numbers increases the amount of spam caught but make sure they're not too low or you may catch genuine email. You might also want to look at the rules_du_jour (search the forums for info) to enhance the spamassassin rules.