3k is usually the cut off point, for both midbass driver and tweeter. There's normally a natural roll off for the midbass driver if IB'ed into the doors... so no, there is no high pass for the midbass with the Infinity passive units. Infinity Reference are known to be bright, usually a peaky 5k to 10k range, which is probably why it's thought they might sound more transparent than a stock speaker. After a while, they can be very fatiguing as well as being dominant over the midbass speaker. If you add an amp, you'll probably notice a better output of the midbass driver. I would also recommend attenuating the tweeter a bit, using the -3db on the passives.

 

Oh I also like to point out that XTC baffles are still essentially baffles because they are in fact, just baffles, they're purpose is not to seal, but to protect your drivers from getting wet... your basket is exposed to the windows afterall.