I think this is an issue to take up with whoever lays out the venue - if the room is set up like a theatre, people should be ASKED to go up front and do their thing, (That way, they know that's what theya er supposed to do.) if its supposed to be informal and in the round, the layout should facilitate that. Don't blame the singers, take it up with the organiser. (Being an organiser, I actually find it very helpful if people tell me what is and isn't working with the layout and venue, I am not omnsicient and need to know what other people think, I am probably not alone in this.)