Adding the mask
Select the material icon in the 'tool panel' and add the mask norm2.jpg into the basic mask slot.
Change the projection to 'Front'
If you do a test IR render you will notice the wrong part is maskde on the floor plane, I had a brain fart and and and did the mask wrong, simply invert the texture in the 'Tone Mapping' properties.
Run IR and the floor should render black, feathered at the edges