Tom-You are correct, 12 is not exactly reachable, I just define reachable a little differently than most. To me, for the purpose of design, if a fair number of players can get within 20-30 yards of the green in two, its "reachable." I hit Driver-3 wood to like 15 yards short of the green, I used a putter from there, so, perhaps unfairly, I deemed it to be a reachable hole. And I wasn't ignoring the site, I mentioned that it would be impossible for the holes I mentioned to happen, but would be cool if that was the case.
As to yardage making the hole and how I play it, it depends. A view of the hole at Barnbougle says it was designed to be played as a par 4 and that it seems to have an Alps feature and a very tight opening to the green. In contrast, the 8th at Oakmont is pretty much flat with a 25 +/- yard wide opening to the green. No, par does not determine, by itself, how I play a hole, architects intent does.