FWIW, I've had a hell of a time dealing with a Surface Pro 4 and multiple monitors. The problem is scaling. The SP4 has a 3200x1800 resolution internal screen, and is quite hard to read with that resolution on a 13" screen. So, Microsoft suggests you turn up the resolution scaling in your display options and scale to 200 or 300%. Now the main SP4 screen looks okay, but if you try plugging it into external 20" or larger monitors, those are going to look atrocious.
So then you might decide to use just the external monitors, and scale it back to 100%. That works pretty well, but Windows forces you to restart (or "Sign Out" and back in, which will close all of your programs and stuff you were working on) every time you change that scaling option. Great! Everything looks fine...until you disconnect the Surface from its dock. Now it's back to looking tiny, and to make use of the SP4 internal screen I've got to once again change the scaling, restart, etc.
People at work ask me why I'm always swearing whenever I come into board meetings. It's because I've just detached my SP4 to bring it into the meeting, and I've either got to drop everything I'm doing to restart and be able to use it during the meeting, or keep the 100% scaling to avoid restarting and squint at my SP4's screen during the meeting.
That problem doesnt exist for me using Win8.1 on laptop and different screens at home and work. Make sure to always use the Win+P "Extend" option, and when first used, select to set the external as primary. Then should work ok. i lost hours to figure this out....same situation as you with need to take my gear to meetings.
It does, if you say "expand desktop" instead of "duplicate". Obviously. Depending on how you lay the screens out there can obviously be regions that are off-screen, that would confuse an app or two (e.g. imagine a 9-digit phone keypad, one display occupying regions 1 and 2, another regions 5 and 6. An app might think to start with its top edge at the off-screen region 4, and its bottom half in region 1, requiring one to hit Alt-Space, M, to lock the window titlebar to the mouse.
