brake resevoir/cylinder position

[rendo]

I have the 'coffin' type brake cylinder/resevoir on my M620ie, i want to rotate the brake lever around so that it points more to the ground. i'd like to get the brake and bars in line with my arms (if that makes sense). this will mean the resevoirs are not sitting horizontal.
question is, do i risk getting air into the hydraulic system by doing this.
if so i may change to separate master cylinder and use the round type resevoirs. i believe this is the arrangement used on the M900/1000 models. Any ideas what cost these cost?

[crust]

As long as the level of fluid does not drop to the bottom it doesn't matter a great deal about the angle.

I've got them on my M900, the early bikes all had them.