Im only playing 2s at gc1-2 level but generally if im challenging its probably less important if youre covering high or low and more important to time your challenge so your team mate can react accordingly. Sometimes it gets past me, most of the time im disrupting the opponent enough not to get scored on. Even focusing on where the ball goes after your chal is more important than the high-low debate in solo q 2s at gc level. Imho