Cancelling Materies with multiple opponents

I can't remember if it has been discussed before.

Harald faces three villains in an extended context (say, a combat). Harald's Close Combat is 5W2.
The Villains: V1=10W, V2=5W, V3=19.

Three opponents implies a penalty of -6 to Harald.

So, Harald has 19W. He has to make a single roll, each villain makes a roll and we take the best result.

If we apply mastery cancellation, I think there is a problem, if I have understood correctly.

Harald 19
V1 10
V2 5
V3 19?, 0?, -1???

My quick decision in the game was not to cancel masteries, so everybody has a bump except V3 which have only a 19.

I missed something?

Regards,

Antonio