You are throwing a lot more shot with steel in a given size than you are with Lead because the steel is lighter, so with that kind of speed and the shot payload you may be shooting behind your birds or lifting your head if you are not bringing them down.
In my case I tend to lift my head and shoot over them - this has been embarrassingly documented BTW!
As wwbirds indicated, generally speaking you want to use open chokes for the larger shot when shooting steel.
Cat