The duplicate reward reduction was removed from all but the very highest rated accounts some time ago. Basically, people with lower ratings were not having literal memory of the positions (and had a larger pool of problems to choose from before seeing duplicates) so it was deemed unfair to reduce rewards for duplicates for most users. It is still in place for the top few players, as they tend to have very good literal memory of positions, and also at the extreme of the problem distribution curve, so have fewer problems to choose from, and without duplicate reward reduction it was hard to control rating inflation in that group, and the top 10 lists would become a memory competition rather than a tactics skill competition. We've also introduced a lot more problems since then which also helped somewhat alleviate the problem at the higher end of the rating pool.
For those that are still high enough rated to get reward reduction, the answer to 2) is that rating penalty would still apply, 'duplicate' is defined by looking across all sets.