RVO agents try really hard not to overlap. They should only do so in very crowded situations.
You can enable the 'locked' option on the RVOController which will prevent it from moving, or you can enable 'lock when not moving' which will set the locked field whenever the desired velocity is zero. However this does adversely affect the local avoidance quality as the RVO algorithm is not originally built for that to happen.
Check out the included example scenes for RVO, those will help you get started I think.
The horizon settings are in seconds and approximately correspond to how far into the future the agent wants to have a collision free path if it continued with its current velocity. A large value will make it avoid things further away, but it may make it too "scared" in some cases. Normal values are around 0.5 to 2 seconds, but those are very fuzzy limits.