It’s really inefficient to use the mouse middle button for navigation, Like if you want to look behind you have to look through the holes one by one. There’s a potentially better design though, as there is already a free-look button in the game. Currently, when you stick your head out the tank, the turret won’t move together with your view if the button is being pressed.
I’d say it’s nice to make the same button work when you are inside too: When you hold the button, your head can move freely with your mouse (maybe just horizontally to avoid confusion and more modelling) and once you release the button, it sets your view to the nearest window. It sounds intuitive and convenient to me.
I honestly don’t understand what you mean by experiencing the map and cleaning. I doubt whether you understand what my topic is as your reply doesn’t seem relevant to this cupola issue. I mean there is the cupola so that the commander doesn’t get shot. Why would I even want to leave the tank by pressing J. I know I can get the better view by sticking my head out, but the point is: the commander may get shot, and the cupola is supposed to provide both view and protection.