If you imagine turning the fretboard around so that the nut was where the saddle is and the frets ran the opposite way, the nodes near the bridge would be in exactly the same place as the harmonics you can find near the nut. A distance of one fret seems to be safe generally - a bit more for the treble strings. I agree with msa3psu though that the plucking point is not the most important thing. In theory there is a node at every point along the string, but in reality most of them are so weak they can be ignored. You can use the same principle further away from the bridge - if you ask yourself whether there is a harmonic the same distance from the saddle as your RH is from the bridge, that will tell you whether you are over a significant node. It may help to remember that the distance from the saddle to the 19th fret is the same as the distance from the nut to the 7th fret - so if your RH was over the 19th, the question would be whether you would get a harmonic at the 7th, and the answer would obviously be yes, meaning that you are over a node. It may be easier to judge where, say, the 5th fret harmonic would be if you visualise it this way.
In reality I think a bit of experimentation is the best way to find out what works.