The defence position does not actually matter that much, if you use any kind of zone.
Not realy. When one is playing 2-3, there are two players at the backcourt and three at the front court. Each has a different role.
Maybe it even needs to be defined more strict - when choosing pressure training with single/two positions, only 1:1 types of diffence should be allowed/count as part of the training.
When choosing pressure training for the all team, then all types of diffence count/available.
What is surely true - this as much more sence than counting the minutes a player played as a center for calculating his diffence as a PG.
It would be a lot of pointless hassle to count how many minutes a player is playing offence and how many minutes he is playing defence. This way it's simple to understand. Playing your C as a PG on offence is challenge enough imo.
It is not hard to caclulate by the user - when a player played as a PG for A minutes, but PG was guarding the SG than count his PG minutes as SG for deffence purposses.
In any case, it will not be hard at all to give both statistics by the BB application at the "Weekly Stats".