Two Masks expanding next to each other problem
I am currently working on a history of Islam video. The green color is indicating an area influenced by Islam. So now I wanted do display a expansion of their influence. I had a map of Medina.

I wanted to expand the influence westwards. For doing that, I had two ai Files imported as Footage, one with the old border (A) (image above), one with the new (B). I placed A over B, then created a mask and expanded the mask until all of B was seen.

This expansion happens over the course of 15 seconds. This 15 seconds represent 9 years. While the expansion is still undergoing, another expansion in the north occurs 3 years after the beginnging, a battle.
Now I have another ai File (C) placed on top of B. I use the same mask techmique. However due to the fact that the expansion of B isnt yet finished, the both masks overlap at the same spot.

You can see in the West on the coast that B is still expanding and C is overlayn on top of B. Because of the fact that the expansion of C happens much faster, it accelerates the expansion process of B faster than history indicates. I was wondering how I can expand two Masks next to each other without this problem occuring. Hopefully you guys can understand my problem. I like to talk through cases, so this is what I did 😉 Any help is really appreciated.
