In the rulebook, the difficulty modifier for PSI powers increases with range - with a +4 for more than 100 meters, if I remember correctly. I find reasonable to think that it keeps increasing with the distance.
However, in the series, we often saw Troi using her powers on people who appeared on the viewscreen - when the ship they were on was probably a few hundreth kilometers away at least. I know Troi is quite good at receptive empathy, but such distances should imply a +40 difficulty modifier IMO.
Is there some explanation of this somewhere(communication technology now applying to thoughts and feelings as well as image and sound, for instance)? And, if not, what do you usually do about it (simply forbidding it, allowing with a high difficulty level...)?
I know Narrators are free to alter the universe and the rules to their convenience, but I am a bit curious why LUGTrek, wich did its best to cover every aspect of the series (and managed quite well), seems to have forgotten that one.
You raise an interesting (and valid!) point. My personal take on this is as follows:
First, since she can actually see the person on the viewscreen, the test becomes easier (to a degree.) Secondly, she probably has pretty good range and we know she has a pretty high psi rating with focus on receptive empathy, so attempting to gauge emotions is, for her, a routine task under normal circumstances. Finally, as ship's counselor, she'll have a decent Medical Sciences (Psychology) skill, further enhancing those abilities. So, when she's watching someone on a viewscreen and makes a statement like, "He's lying" or "they're worried," we only assume it's her empathic powers. In reality, it's probably a combination of receptive empathy and her psyche training.
In game terms, for something like the above situation, I'd start at the Almost Impossible level due to range, lower it to Difficult because she has visual contact, and either lower it once more to Challenging for being able to use Psychology OR add the player's Psychology score to the Receptive Empathy score and the die roll. I know it flies in the face of what the rule books say, but if the empath is merely watching, I would allow for a Focus modifier because he/she can concentrate exclusively on that part.