why is my wifi speed slower when the router is on the same desk as my laptop or phones? (but runs much faster when thy are at least 6 feet away)

why is my wifi speed slower when the router is on the same desk as my laptop or phones? (about 200 to 220mbps)

if I put the laptop or phone at least 6 feet away, then I get much faster speeds, up to the full 300mbps tier that my modem is subscribed to.

thanks!