That depends upon your provider and where you mount the "eye." With my DirecTV mini-genie mounted behind the TV, I don't have to be straight on, but I need to hold the remote on at least the same side as the "eye." Go to the opposite side and point to the back of the device and no luck.
I can't speak for the boxes from all providers, but with Verizon Fios and Comcast Xfinity boxes, the remote is able to transmit/receive signals through box even when it's mounted behind your LCD. If your box can't not be accessed by the remote, you can purchase one of the Infrared remote cables from Amazon and it basically plugs into your box on one end and other end has a little sensor device that sits on the side or top of your LCD so your remote can access it. Just make sure the Infrared remote cable is compatible with your box.
I have this mounted on the wall completely hidden by a wall-mounted TV. Have not had a problem using a remote to initiate any function of the Cable box. It is in a small guest bedroom so the signals may be bouncing off the walls.