Is there a way to 'limit' the shadowcatchers range in Blender 2.8

I am trying to render out a box with the shadow that its casting on the floor. The rest is supposed to be transparent (client is going to use it for compositing).

When I use the white backdrop as a shadowcatcher…the final render is giving me a very light shadow across the image (apart from the obvious shadow). So the image isnt completely transparent. I have added the render to a white background in photoshop:

So the shadows that i want, are circled in blue… but outside this…i want it to be completely transparent. And its not…just look at the part that is circled in red…you can see that the left part is a bit more grey as oppsed to the right part (which is pure white that I added in photoshop)…I know I can mask the shadows that I dont want out in Photoshop… but Id like to know if this is possible in Blender.

My question is:

  1. is there a way to ‘limit’ the shadowcatchers range… or is there a way to light the scene in such a manner that the shadows arent all across the image?

  2. second question: is there an easy way to control the intensity of just the shadows, and not the rest of the image…?

You can add a rectangle with a hole in it in front of the camera, visible only to the camera.

Thank you for your reply @CarlG

Ill try to figure out how that works

Regarding the second question… Can you help me with a node setup in the compositor to control the intensity and blur of the shadows? I probably need to render a shadow pass…but other then that im stuck on how to set it up