Flipper is an IR (infrared) remote control. It requires direct line of sight to operate the TV and STB / cable box.
While it may appear that there, if you are using the Xfinity remote to change channels, then there is a box, most likely a small whte box that may be installed on a wall or behind furniture.
If your box is not in direct line of sight and you cannot move the box, then then get an IR - RF extender extender like the below, or similar products at Amaozn or BestBuy: