I was in an infantry recon unit back in my days in her majesty's service, and our long landies all indeed had a MAG pintle mounted in the middle, right behind the front seats.
My suspicion is that this was done because with the canvas hood built up, there was still a way to stand up and man the gun, through an especially applied flap in the roof. Would have been decidedly more difficult in other positions.
Additionally; this indeed allowed for more guys and gear to be transported in the rear, and communication between the observer/gunner on top was easier with him close to the driver and patrol leader. Especially when going flat out on dirt roads.
I remember having to completely wrap up when in those things because sand is course and gets everywhere and stuff. In winter, being on top was inviting frostbite, so nobody did that for more than 30 minutes before switching positions. And your entire mug covered by multiple layers of cloth made communication difficult enough already without having to shout across an additional meter or so to the guys up front...
The range of fire was never a real issue; the front arch was 100% covered, and if you were shot at from the rear you had either probed too deeply into enemy territory or were bravely advancing to the rear anyway

To be honest; Firing archs never really were an issue and it never came up that we'd need to project into the rear arch...
I'm running a T2K campaign right now and my players started out with exactly that type of landrover, pintle and all. I blew it up for them, but they did make good use of it (and the pintle) when they still had it.
Also: recoil-challenged would be a better term
