Technically - the flaw in the slaw is the fact that your antenna bracket sucks.
When you mount a antenna, you want to mount it as far away from anything metallic that could reflect the signal as possible.

The bracket you have is the lazymans way of installing a antenna.

In order to attach the antenna to the bed and make the bed capacitive, you would need to attach 4 copper ground straps at least one inch wide - braid to the 4 corners of the bed to the frame and 2 to the cab and 4 from the cab to the frame and two from the front sheet metal to the frame and one from the engine to the frame and one from the transmission to the frame and one on each corner to the axles to make the body appear as if it was one solid object.

The problem with this is - most people are cheap and lazy and refuses to spend money and does not understand how transmitting works and omits these difficult steps from the install.
After they install it and finds that it does not work as designed, they blame the mount and got to some other type of mount or antenna.