Prob with torpedo solutions (again)

[Echo76]

I make this quick: @ longer ranges (4km or so) I tend to miss crapload of torps by the ships bow even if I use the cross the T approach. What I've noticed that if I select 2kts less speed than indicated by map update I get excellent hit ratio, any idea what might be causing that?

P.S. @ same range, would +/- 100 meters error in range be critical, I really suck in math.