DisplayPort Daisy Chain on Ubuntu

I have the following set-up, as described in the DisplayPort DaisyChain FAQ. Note that my two monitors are different to each other (is this an issue?).

Computer video DP out --> DP to mDP cable --> #1 U2417H mDP in (MST On, DP1.2 On)
#1 U2417H DP out --> DP to mDP cable --> #2 U2414H mDP in (MST Off, DP1.2 Off)

Both monitors work however my issue is that the system only detects one monitor - and hence it just shows the same screen on both. In my display options I can't change the screens to extend, as it only detects the one screen.

I followed the steps below and set MST on and DisplayPort 1.2 Enabled on #1, and DisplayPort 1.2 Disabled on #2 (there was no option to turn MST off).

* Press the monitor Input Source Select button
* Highlight mDP or DP (whichever you are connected to)
* Hold the green check down for 8 seconds
* Disable DP 1.2/MST to set it to DP 1.1 or MST Off

My system:
Ubuntu 16.04.4
AMD Radeon HD 8570 with Radeon driver

I would like to have both screens extended, rather than mirrored. What do I need to do to get this to work?

Thanks