Here’s question that most volleyball coaches have to answer at one time or another. Do you use your libero to play in Position 5 or Position 6. That generally means address the case of the libero playing back row for the two middles. It is part, however, of a broader question of how to maximize your back court, both offensively and defensively.
The decision involves three primary considerations.
Back row attack
Generally, if you want your back row OH as an attacking option then you probably want them in Position 6. Because that usually (but not always) involves them taking up a deeper position, it means they are better able to get a good approach for their attack. It also provides a bit more attacking flexibility. This is especially true when working in combination with a front row quick attack (e.g. running the bic or back row quick). Having them playing in 5 limits things.
Second ball setter out-of-system
In the situation where the setter has to take the first ball, who takes the second? I wrote about the setter-out setting question previously. If the player in 5 is expected to take the second ball then you have to think about whether a back row attack is desirable in your scheme. If so, then having your OH setting isn’t desirable. There is also the question as to who’s going to set better ball to the front row players, which is more of a personnel question than a system one.
The other consideration has to do with how you’re setting up your defense. Will most balls tend to go to 6 or to 5 in your system? Is there a meaningful difference in the digging ability of your OHs vs. your libero? If so, you may want to favor one or the other defending in the zone where more balls go. But keep in mind the question of the purpose of defense.
Different situations, different schemes
When I was coaching the Exeter women in my second year we played a system where we left one MB in and only used the libero on the other with both playing in 6. My reasons were because I had OHs who were strong reacting forward into the court (good for playing in 5), but not strong moving laterally (needed in 6), and we didn’t use them much for attacking back row as the MB and setter or OPP could all take those swings. When I was at Svedala our OHs played in 6 for attacking reasons.
The bottom line is that you need to think about your team and your players and go with what maximizes the effectiveness of the personnel.