On any given forum that discusses firearms and related issues you will find a plethora of discussions about what people carry each day; what kind of gun, how much ammo, what knife, etc. What you won't find as many of is discussions about how the gun is carried or, maybe more important, where. I happened to have a recent conversation that revolved around holsters and the best way to carry a concealed weapon. When circumstances became part of the conversation I was surprised to see my conversation partner - a veteran law enforcement officer of almost 20 years - get a blank look on his face regarding how different circumstances might dictate different carry positions. He'd never thought about it. He put his holster on his belt, his gun in the holster and went about his day.
Given that about 92% of the population is right handed, probably the most common place for carrying a gun is on or near the right hip. Why? I'd venture to guess that - at least for off-duty cops - we're so used to carrying our weapon in a duty holster on our right hip that it's only natural to put it there off duty as well. It makes sense. We're used to knowing that the gun is there; we have the movement to reach it mastered. Whether we move the holster a bit forward or a bit back, or put it there using an in-the-waistband holster (inside the pants), it's still in the same general location. Concealment is usually not too difficult. In summer months the cops are all the guys wearing Hawaiin shirts unbuttoned. In cooler months we're the guys with sweatshirts or jackets - like everyone else. But in some situations this position for the gun makes no sense. Have you ever sat seat-belted into the driver's seat of your car (or passenger seat for that matter) and tried to draw your gun from this holster in a timely fashion? Good luck.
If you need to keep your gun concealed but be able to get to it from that seated position there are several better options. A cross-draw holster makes your reach easier and since - most of the time - the threat will likely present itself from outside your vehicle on the side closest to you - if you're the driver, then the gun comes out almost already pointed in the necessary direction to engage the threat. Other options for concealing your weapon but still having it positioned across your body would be a shoulder holster or an under-garment holster system. Under garment systems include belly-bands and truss systems. This brings into question the position of the weapon in the holster when you're wearing any of these: shoulder, belly-band or truss system holsters. Belly bands and truss systems - as far as I know - restrict carrying your weapon in a vertical fashion that requires an upward drawstroke. Since we're talking about being seated, getting your outer garmnet up and out of the way to get your weapon out might be a bit complicated. A shoulder holster would be better but even those present three different weapon positions: butt up, butt down or horizontal (butt forward obviously). The most desireable would be horizontal (in my opinion). Butt up or butt down both require clearance for a draw stroke - clearance that might not be there or that is difficult to create if you're seat belted in. When moments count you want the fastest access to your weapon possible.
Another option that can be explored - but that is really uncomfortable to me - is carrying your weapon in a discreet belt bag, or what we used to call a "fanny pack". Since this positions the weapon for an easy draw and also keeps the muzzle pointed at the door (for right handed folks) it might be a suitable option. However, it takes two hands to get the gun out and there's not a lot of space available (typically) between us and the steering wheel. Yes, some skinny folks with long legs might have an easier time of it, but you still have to get that weapons bag open and have room to get your weapon out quickly.