I too noticed a problem with the shot when I was playing with it.

Either the viewport is very close to them and small, which makes the gun very small indeed and strangely inside the window, or the officers are on a platform far away from a very big open space (like a docking bay) and the gun is much bigger.

It's really difficult to make out as there is no detail to establish which is correct (it's very dark which doesn't really fit into the design ethic of the Tantive but that doesn't rule it out).

I thought the port was situated in the bottom of the Star Destroyer hanger frame or the smaller forward hanger as they seem to get a downward view of the escape pod but the Tantive isn't visible but that does pose the question of where the planet is.

If that is the case being a space ship it doesn't make my mock-up impossible (indeed in the battle of Endor we see an 'upside down' Star Destroyer) but it would buck the general trend of having Star Destroyers pointing bridge side up (relative to the camera).