Okay, let me preface my answer with my own military experience. You may thinking about this too literally. They would not have to necessarily be using the deflector array as an exit. They could be leaving via a number of means you may not consider on the face of thinking about it.
Starships need exits, lots of them
On our current Earth, military vessels that are designed for combat, not necessarily comfort, portals to the outside of the hull can be found in strange places. Sandwiched between two spaces doing other kinds of duty where an exit is considered strategically important if you need to escape those spaces, but may not be used otherwise.
On a starship, particularly one as tiny as the Defiant, (about 170 meters long) I can see the surface of the ship being dotted with a variety of places where an extending tubule could connect and seal a docking connection between two ships or a ship and a station. It would likely be very small, two meters or less, but certainly enough for crew members to leave one at a time on a built-in ladder. Since we don't ever see them leave via the docking bay, we are not privy to the process.
Now given that the entire nose of the ship is inside the hanger bay, it may simply be easier to seal the ship in via force field, and pressurize the part of the ship inside the field. Then ladders could be extended or moved upward and allow egress while inside the station.
Looking at official schematics, no official markings indicated airlocks or escape portals but that does not mean they aren't there, it just means most people are looking for photon torpedo and phaser arrays and as far as production goes, if they don't use it, they don't bother to mark it.
Seeing how the Defiant is small enough to fit inside of a starbase of sufficient size, it makes sense for it to have landing gear and exits strategically placed all over the ship for ease of access and to enable maintenance to be done.
You aren't the only person with Defiant technical issues:
Here is a quote from a Star Trek fan-site, I respect, Ex Astria Scientia and in this case agree with after reviewing dozens of official schematics as well as fan-generated ones:
The Defiant Problem:
It is hard to believe and hard to accept that there are no reliable technical specs on the Defiant, unquestionably one of the most popular starships in the Star Trek Universe. It is most unsettling that not even the ship's size is certain. Depending on what is taken as a reference, its length seems to vary between less than 50m and close to 200m. This means an uncertainty of 400% for the length and even 6400% for the volume! Since the DS9 Technical Manual with seemingly accurate deck layouts was released in 1998, the confusion is complete, for the plans conflict with the numerical size figures in the same book.
In addition to the size dilemma, there are a number of problems like the uncertain armament, the location of the impulse engines, the existence of a landing gear or the registry number of the new Defiant (ex-São Paulo NCC-75633).
Using the image below they are leaving via the forward docking airlock which appears to be on the same deck or above what is labeled as the mess hall in the forward part of the ship above the deflector array. In my experience, this makes perfectly good sense and seems reasonable for a ship of this size. There should be several other easy access portals including the cargo bays, the shuttle bay hanger, the warp core section and engineering sections of the ship, the port and starboard nacelles as well as any weapon control point.