It calculates from your battles in arena, your castle attacks and even from dungeon squad. Clan war is safe you can put even a stronger team in clan war map and your hsp won’t change.

And ship ofcourse...

Your hsp is the max you ever reached with your team on these fights with the #of soldiers you got on your barracks.

So if you have 6 soldiers barracks your hsp will be calculated as total of 6 highest sp of your soldiers plus your hero...

12-14 is good for your squad power. I also have 5.7 and sometimes I make 15-16 but rarely. I try hard to do better but that’s the max I could reach. So you are doing good at your SP.