Applying mask in bin space

I'm currently trying to apply a mask on a simulation with the parameters x-bins = 981 (168.7 mm) y-bins = 1043 (179.3 mm)

When I apply the mask with the method

simulation.addMask(ba.Rectangle(xlow,ylow,xup,yup))

and want to input ba.Rectangle(0,0,100,100) a large portion of the image is being covered even though I want to use the bins as the unit of measurement. What do I have to do in order to achieve that? I know that for spherical detectors one can just multiply the values by writing ba.Rectangle(0*deg,0*deg,100*deg,100*deg). Is there a similar approach for the bins?