With our Home dircectory occupying the F drive, (don't ask me why the f
drive is selected as the home, that was before my time) and A-E being used
up by physical drives, the usb thumb drive then takes the F drive value but
cannot be used because the F drive is lying on top of the physical drive.
You have to go into Disk manager and change the letter of the USB drive.

What affect would there be to change the home mapping to another letter
lower down and keep the "First Network Drive" value in the client set to F
(NO_DEFAULT is used and the sys is mapped to Z). Is the First Netowrk drive
even used in such a scenario?

In my testing I found that I can remap the F to U and then the USB is found
fairly easily. I just don't know if there are any issues to worry about
with the First newtork drive setting.