POWERLINE 1200 NOT PROVIDING LINK SPEEDS OVER 60MPS

I recently purchased the Powerline 1200 devices (4 in total).  I have one connected directly to my Cable modem, 1 connected to a lPC in the same room, 1 connected to a PC in an upstairs room, and 1 connected to a WiFI adapter also in an upstairs room on opposite of house from modem and the first 1200 device - Say, 50-60 feet away

The ethernet and link lights on all the decices are solid green.  However, I'm seeing some very odd behavior when it comes to actual speeds at each location.  If I run speed test from my modem, I'm getting nearly 800 Mbps download on a 1Gig cable circuit.  Typical and expected.  

On the Powerline 1200 which is in the same room on a different outlet I'm getting only 100 Mbps.  On the 1200 upstairs connected to a PC I'm only getting about 70 Mbps tops, and on the one connected to the WiFi adapter if I use my 5G band, I can get 300 Mbps.  

Why the drastic difference in speeds from each of these devices?  I would expect distance to have some affect but that much?  Could the outlets beign on different power circuits have an impact?   Looking for any info which may help improve the speeds I'm seeing.