There are, effectively, three kinds of upgrades after check-in opens, though (AFAICT, as I've never been able to take advantage, either flying in highest cabin or in a group larger than the number of available seats in the higher cabin)

* OLCI upgrades, which are custom priced by AFKL (they at least appear to net out paid seats (thus a Platinum tax)) and don't seem to be consistently offered for miles on awards
* Counter upgrades, which have two tiers ("purgatory") of prices based on customer profile; these may or may not allow upgrading for miles on awards
* Post-boarding, which seems to be a fixed amount per route and doesn't issue a new boarding pass (thus no lounge access, unlike the previous two) but once aboard, there's no distinction between revenue and award (there is a practical distinction between non-rev and the others, though...). The fixed amounts seem to approximate the lowest possible award price for the route in the higher cabin.