Maybe I may do an error, because I do not play by forum but I have read as the forum dice roller works. The number after the @ indicates the attack value of the dice. Hypothetically the hit value should not influence the result of the “dice rolled”, which is always a d6. The problem is that rolling a d6 with an attack value of 13 it is impossible to have a hit confirmation from the dice roller. It is still possible to asses the hits with “human intervention”.
In such situation, the, the 2@13 are two d6 rolled for the two infantry and should be considered ok. If one of them score a a 1, it should be a hit. So the only thing to do is to roll for the 3@3, for having the fighters outcome.
As I said, however, I am not an expert of forum dice rolling, so a more qualified opinion is needed! :-D