Yes if using those tripoles as heights you'd need to angle them with brackets. And I'd be concerned of such a heavy speaker that isn't flush against the wall (something like 18kg?
The surround speaker should have some degree of angle regardless so the tweeter is pointing sound towards the ear unless its designed to have an off axis vertical response (the Arendals aren't, I remember them being around 20-25 degrees)
A surround speaker needs to:
1. Minimise head occlusion effects (do this by mounting it higher)
2. Not provide clear localisation (processors and setting the right levels can normally do this but some people like to try tripole/dipole; maybe benefits tiny rooms?)
3. Provide accurate sound to how it was designed by either being designed to be really good sounding off axis vertically or angle the sound to the ear (most speakers would clearly benefit from an angled baffle or a tilt via bracket)
4. Still provide excellent detail to embody the surround track (you can do this by being in the sweetspot for the best on axis response vertically and horizontally)
It's actually really easy to do.
Sit down with a speaker where the tweeter is higher than it means to. Then just lift your seating position so you are now in line with the tweeter. You'll most likely get a much more clearer, accurate sound. It's really not rocket science.
The bigger the room, the bigger the dispersion if you're far from the surround speaker which means being on/off axis is maybe a bit more irrelevant. Its very easy to make the case that actually the smaller your room, the MORE Important you should be on axis re: sound because the dispersion is going to be far more limited re: angle to your MLP.