I have to say, I really do not understand these KUP fares at all, despite having tried a few times. Am I right in saying that they (KUP and YUP) are like full-fare economy tickets with an upgrade supplement, and that since so few people actually pay for full-fare First in the US that you enter the cabin ahead of all the AA Platinums / OW Sapphires etc who would be auto-upgraded anyway?

And as per the earlier question, where do I book them / identify them?