I feel sort of foolish asking this, but the new rules text for Combat Expertise is the following:
You can choose to take a –1 penalty on melee attack rolls and combat maneuver checks to gain a +1 dodge bonus to your Armor Class. When your base attack bonus reaches +4, and every +4 thereafter, the penalty increases by –1 and the dodge bonus increases by +1. You can only choose to use this feat when you declare that you are making an attack or a full-attack action with a melee weapon. The effects of this feat last until your next turn.
So, after your BAB hits +4, and you take a -1 penalty to receive a +1 dodge bonus, is this immediately adjusted to a 0 penalty for a +2 bonus, or do you always have to have some sort of penalty?
Combat expertise clearly states that the penalty increases by -1/+4BAB.
This means -1TH/+1AC -> -2TH/+2AC -> -3TH/+3AC and so on...
You also cannot scale how much you use the feat, it's always the same depending on you BAB.
Ah, critical reading failure on my part. Thanks.