you don't understand form 8959.
8959 line 18 is the additional medicare tax you owe (probably $2443). this flows to schedule 2 line 8 and thus increases the taxes you owe. *($2443 + $388 from form 8960 = $2831 that's showing up on schedule 2 line 😎
8959 line 24 is the actual additional medicare tax withheld. this flows to 1040 line 25c and thus decreases the taxes you owe
