Don't put it directly behind the camera, as @looney2ns mentioned maybe at a 30 degree angle. Just be careful not to blind the cam with IR or have it too close to the subject so you don't washout or splash back. You can play with the final positioning during an early evening by seeing what the cam is picking up with the extra IR spread and adjusting accordingly
Does this IR light have to be behind the camera or can I put it somewhere else in between both cameras but up higher? I have one camera sitting on my car (about 25’ away pointing at the front and side of house n one on the rail of front deck right in front of house. I would like to maybe get someone to hang the IR light from a tree or somewhere up higher because right now anyone can come along and take the camera off my car.