I've had similar issues with scaling on multiplicity and I have a solution that works great for me. Download a portable program called HRC.
http://funk.eu/hrc/
It changes resolutions with a hotkey. Set up your 4k resolution to one hotkey and your 1080 resolution to another. Once you connect remotely to that host, click your hotkey, and it instantly changes. Change it back the same way.
Good luck.