Did you have the Rifles walk from far to close range, or did you start them close? Just curious, and I think rifles are pretty good, especially late game!
In all cases I spawned them and faced them so that they were already looking at each other, to avoid any "model has to turn around, taking a few extra shots".
Walking is a weird one too, since you may potentially expose 1 model to concentrated fire depending on the squad's formation, so they were all already in sight of each other before I switched one of the squads to 'enemy' and had them shoot it out.
I imagine in any fight the approaching squad is always at a disadvantage, cover or no cover, if only because of the moving accuracy penalty and the free few shots the defending squad gets on whichever first two models get past the threshold of max range for the defenders.