Originally the raid leader put a group of 7 raiders, granted I explained to him that 10 is the minimum and in my opinion please make it that people can't queue, unless there's a minimum of 10, because there will be random pugs that will attempt to run in small numbers. Also, I couldn't tell if the adjustment worked when the group size was 15 players and dropping down to 12 because some people decided to dip out before we pulled was being scaled in difficulty or at least in mechanics. It felt much harder as people left and felt like we were contending with the larger comp size of 15 than 12, unless that required us to leave instance group and rezone is that intended?
Creature health and damage should scale completely dynamically as people come and go, as well as mechanics interactions such as the number of puddles into which Immerseus splits. The number by your minimap should be an accurate indication of your current instance group size.
For testing purposes (mostly internal convenience on our end), you can currently queue with a fairly small group, but nothing will actually scale below a 10-player size. When we release 5.4, we're intending to require a minimum of 8 players to queue. The thought there is that you might want to begin clearing the instance or at least zone in and get ready while waiting on a latecomer 9th/10th, and if we set the queue limit strictly to 10, that wouldn't be possible.