...on the close hauled thing, it matters, if you're beating to a mark, close hauled is your proper course, and you shouldn't be on stbd beam reach all of a sudden messing with a port tacker. If you're reaching to a mark, there is a lot more gray area about proper course...
Two observations:
1) You are correct that "proper course" is a big gray area. It is defined as:
A course a boat would sail to finish as soon as possible in the absence of the other boats referred to in the rule using the term.
If you can make a reasonable argument as to why you would have sailed that course even if the other boat weren't there, then a protest committee is very likely to conclude that you sailed your "proper course". It is entirely possible that two boats sailing the same leg in the same race would have two different "proper courses". Pinching vs. footing, sailing hot vs. sailing deep, sailing for wind vs. sailing for current, etc. are all considerations that yield different proper courses.
2) The term "proper course", only appears in two rules, RRS 17, and RRS 18.4. It does not apply to boats on opposite tacks on a beat to windward.
Regards,
Eric
