Tracon Controller reported that when an Airbus followed a B744 on the same SID; aircraft performance characteristics led to a compromise in separation. The result was a 'wake remnant' violation.

Narrative

I was providing OTJ to a Controller in training. Traffic was light; but we were in the middle of a runway change. Aircraft X departs Runway XXL on departure SID; a left turn toward VOR to intercept an outbound radial to the south. Aircraft X was turned to a 090 heading and climbed to 7;000. Aircraft Y departs next; on the same SID; but since the A320 rotates before the B744; he turns inside the track of the B744. Aircraft Y is also turned east; 100 or 110 heading I think. I have not listened to the tape yet. Again; the A320 performs differently and turns pretty quick; therefore cutting off more of the track of the B744. This; I believe; is not realized by the trainee. I place a j ring on the B744 and we are very close. I take the frequency; call the traffic and ask Aircraft Y if he has it in sight. Aircraft Y acknowledges that he does and I instruct him to maintain visual separation; caution wake turbulence.The question now is if I was able to apply the visual separation before I lost separation. It may have been lost before Aircraft Y was turned. But since we turned the Aircraft X off the SID; I would have to assume that we buy it; not the tower. The loss was a remnant violation. 4.99 miles when 5.0 was needed; and I think the A320 was never less than 1;000 below the B744. That is what I don't understand about the whole remnant issue.