Prime tower strange behaviour?

[rafpigna]

Hello
I dont know if I never understood the Prime Tower behaviour and functionality, but I'm really struggling to understand what is happening in one of my prints

Please check the screenshots below

In the first screenshot I have a small cube printed in two colors, RED and BLACK, and the resulting Prime Tower is about 25x10 mm

On the other screenshot, I have the same object in the same two colors but I also added other 8 cubes, but printed in just ONE color, BLACK. The resulting prime tower is way bigger!
Why?
In my understanding, the color changes that the printer has to do is the same in both cases, and the amount of the red material that the printer has to use is the same in both cases, since will be used only for same cube in both cases!

So what is happening with the Prime Towers? Why is so big compared to the first one? In my understanding should be exactly the same!

I did some test and basically, for any object that I will add on the plate, the wipe tower grows a little bigger each time, and I didnt understood why, since the color changes are always the same each time!

Is this right or it's a bug?
And if it's right, some one could explain me why this happens?

Thanks!