Most 6.5" component sets I've come across are designed to be used in an infinite airspace, similar to infinite baffle subwoofers. The airspace in the door is large enough to create this effect. In my experience speaker baffles tend to hurt low end extension and create strange peaks in frequency response. With the baffles the voice coil has to work against the rebound created by the sealed airspace, so it lessens overall driver extension (the cone can't move in and out as far).
There are a few things you can do in order to gain more midbass and better overall frequency response from your existing setup depending on how much work you're willing to put in.
The first thing and easiest to address is canceling out "backwaves" (I can't recall the real term), which are basically the sound that comes off the rear of the cone. Ported enclosures use these waves to essentially double output by porting them out of the enclosure in phase with the front sound waves. This is why ported boxes need to be built with the correct airspace/port length/etc. Waves out of phase with each other (like the ones that can leak out of the door) can distort sound and even cancel each other out to an extent. Sealing off the openings in the door panel just to help prevent these waves "leaking" out helps, and even better is to use some sort of sound-cancelling material directly behind the speaker. The triangular shaped foam pieces work well, but even something as simple as a styrofoam egg carton can be repurposed to help a bit. This just helps reflect those "backwaves" into each other to cancel out some of the sound, and also helps prevent those waves reflecting back into the car.
Past that you will need to get a little more creative. The stock speaker mounts are thin plastic and are unfortunately awful for good speaker performance. Removing them and replacing them with a wooden speaker mount can help, how much is dependant on the speakers and the vehicle. I just used some 3/4" MDF for mine and made a ring I attached to the door, and then attached the speakers to. This helps bring out midbass more than any of the other frequencies.
It may also help to list your head unit and amplifier, along with how you adjusted your amplifier's gain/what frequency you set your crossover to. Sorry for the long-winded explanation, I tend to ramble when it comes to car audio.
