Which booster? Mobile Pro 4g? Did it ship with the small mag mount external antenna? The mag mount takes very little metal to work. The small mag mount has very little negative affect across all frequencies. If it's the Mobile pro 4g, five feet distance on the internal antenna is being generous. The device is advertised as up to 50db gain. I see average 35db gain.
I helped install a house based system at a friends place. We placed the 4g myfi next to the internal antenna. He went from barely 1x to solid 4g internet for his work computer.
I also have the Wilson Sleek. It averages 18db gain.