BarBar Jinkx said:

I always thought they were at the back of the base at this point (bare in mind the falcon just flew out of there a few moments ago if memory serves me correctly) so if the cave entrance was changed slightly it might make more sense.

and for the record - I Fncking LOVE the new shot

Leia explains earlier on in the briefing scene that this is a different entrance. You can also see that the transports are housed in a completely different hangar than the Falcon. The hangars are all over the place and connected with all the tunnels we see. Plus it's been mentioned that there should be only 1 transport as 3P) says "Your highness, we must take this last transport". Well this isn't a mistake by adding 2 transports. In the briefing Leia says this: "All troop carriers will assemble at the north Entrance.The heavy transport ships will leave as soon as they are loaded." So what we see here are the heavy transport ships and not the troop carriers.