Bid for upgrade question

Happy New Year!

I have the option to bid for an upgrade (current upgrade price is £1888 for PE to UC JFK-LHR, no thanks). I was wondering if anyone knows what fare code the ticket is given if the bid is successful? Does it depend on the remaining number of tickets for that fare bucket in the cabin on the day?

The only reason I'm considering it is to bump the tier points, so would hope for something other than a Z.

Thanks all!

I bid for an economy upgrade to Upper last March. Missed out on the bid, but when checking in was offered an acceptable price. Got 200 points for upper one way.

Thanks, David!