Your post reminds me of what a good spearfisher I knew in Cuba said to me once about this sort of thing "The fish that is yours no one else will take it.". I guess it's a way of taking the pressure off yourself. I don't know to what extent I believe in that as I've definitely seen guys shoot a fish from under me, but then maybe the fish wasn't really mine in the first place
Nowadays I don't mind if I'm not the first one in the water even on a small spot. The only exception is if I'm with new guys and I think they'll shoot something silly and disturb the other fish. If I'm with experienced guys I don't mind at all. I know that chances are the commotion will attract some other fish and if it's a pelagic they know to leave it there for a little bit to increase the effect.
If the area is larger I normally don't mind someone getting ahead of me. I figure if they're so keen on doing so then they will shoot the first fish but then I'm under no obligation to spot them as they're handling the fish and move ahead significantly by the time they brought it under control and put it on the stringer so I get the next one.