What is the reason for this change?
If I understand correctly ... a map of 4800 pixels at 5 map pixels per meter equals 960 meters. If increased to 8 map pixels per meter ... then it equals 600 meters.
So, with the newer scale you are kind of zooming in ... but in doing so, also decreasing the distance a map is simulated (within the same pixel map size) compared to the previous scale.
On a 1600 x 900 screen, the maximum firing distance seen from a unit at screen's edge to the other screen border is about 320 meters with the TLD scale ... so I'm assuming that distance will be proportionally less using the new scale.
Is this correct, because being able to fire over long distances is an advantage CC has over other games.
The short answer is, yes, that is correct. There are basically two factors in changing the game scale:
1) It allows us to bring all the game elements (terrain, soldiers, vehicles) to basically the same scale.
2) It allows for higher resolution and thus more detail on the terrain graphics, game effects, etc.
You're correct that the net effect is to 'zoom in', and you will be able to see somewhat less of the battle area on the screen without scrolling. This is the trade off for increasing the resolution in the CC engine, which doesn't have any practical way to 'free-zoom' to any arbitrary distance / resolution. But overall, with the higher screen resolutions available today, you can still see more of the battle area than when the game was originally released, and hopefully it will look a lot better.