Motion Detection: Sensitivity vs. Threshold
There is no clear cut answer to sensitivity/threshold settings that can truly eliminate false positives, while maintaining that they trigger as desired, for all cases. The problem is simply that everyone's cameras will be looking at such drastically different scenes, that one person can have false positives on a very low sensitivity (due to snow) whereas the other can use the same settings and not even catch the movements of trees in the wind.
The best thing you can do is work out a configuration for each camera based specifically on what your cameras are likely to register as motion and customize your settings to your preference. In order to do this, it helps to understand a bit more about how sensitivity and threshold work.
Think about it this way: sensitivity is a measurement of the amount of change in a camera's field of view that qualifies as potential motion detection, and threshold is how much of that motion needs to occur in order to actually trigger the alarm. It can be thought of like this: for however long there is enough change to satisfy the sensitivity parameter, a threshold meter is silently being filled up until it hit's the trigger point.
Considering this, if you set your sensitivity to 1 and threshold to 100, it would be practically impossible to trigger a motion alert. Alternatively, if you set your sensitivity to 100 and your threshold to 1 or 0, this means that the slightest change could set off the trigger. The trick is to finding a healthy balance based on all the factors that stand to stimulate your motion detection sensors and doing your own personal testing.
A practical application of this would be, for example, a check out line in a grocery store. People don't want every person walking in and out to trigger the alarm. But if, for some reason, one of these people starts dancing or attacking another person, the degree of movement and activity would trip the threshold meter. This feature exists to give users complete control and the ability to both fine tune and customize their motion detection settings.