It's hard to tell really. If the barge was bigger it basically means more leanient constraints for the final approach, which could result in a softer landing. Remember that Falcons can't hover and thus have to achieve perfect timing for the final burn. If you constrain time down to almost zero and space down to a few meters and the initial velocity is terminal velocity + pretty fast horicontal movement, it's almost a wonder that they're already doing what they're doing.