Problems with download speeds / throughput on Hotspot / Home Internet Devices

I have been attempting to troubleshoot issues with download speeds, i.e. overall throughput when performing a speed test when connected to my Unite Hotspot - now AT&T ZTE Home Internet Device, and tethering to my Note 3/Note Edge Device.  Simply put, the devices intended for internet sharing seem to have a cap/max throughput avg of 10.5Mbps, where my speeds via tethering to my Cell phone(s) pulls in an avg of 31Mbps.

I have tried to work with AT&T ATS to help with this, and the answer I get is "the speeds, while much much slower than your phone tether, are within the acceptable LTE range".

I understand that the devices are transmitting at the lower end of what is "acceptable", but that doesn't answer the question on why the devices are 50-60% slower than a phone-tethered connection.  I'm paying for the Hotspot devices, so following AT&T's suggestion of just using my phone-tether as the primary internet connection isn't really an answer I am happy with.  Also, I followed their suggestion to move to the Home Internet device, but this still yields the same results.

Other answers I have gotten from ATS: is that there is interference in the area causing the problems, and that the Hotspots don't transfer and transmit speeds at the same rate my phone does.  Are AT&T data-only devices really rate limited or incapable of speeds above 10-14Mbps?

I'm not trying to turn this post into a complaint post, though I am pretty frustrated dealing with this issue and with AT&T's lack of 'want' to assist.  And while the speeds might be acceptable, the point is that there is a definite gap in throughput between devices.  That is really what I am interested in understanding.  Is this anything anyone else has noticed?  My location and connection device details are below.. I'd really appreciate anyone elses' input and help on this.  Thanks!

Location:  West/SW Las Vegas, NV.  CID: 19721

Signal Quality:  5 Bar Signal Quality, -71dBm, connected cell tower is about .2 miles from my home.  A second tower is about .5 miles from my home.

Devices:  Note Edge, AT&T ZTE Home Internet device (upgraded from Unite Hotspot).