All tickets in the PNR must be in the same fare basis. Thus, if there are only 1 or 2 seats at the $1,500 fare basis and you select 3, all 3 will price into the higher fare basis.
There is no need for "shenanigans" here. Simply go on the HA website and try booking 2 seats. If they both price at $1,500, book them at that price and then book the third eat at $2,100. If you can't get two seats at $1,500, book 1 and then book the other two at $2,100 (or whatever pricing you can get).
There could be as few as one seats at the $1,500 price, so don't delay as if someone else books that one seat, you are SOL.