[Paul Riley]

Of course,long range shots are possible,even beyond visual range,but as you imagine the margin for error at these ranges is extremely high.You have the possibility of premature detonations,it may not hold its depth and drop before it hits anything,your settings could be out by just a fraction,but at extreme range this would be proportionally much larger.You may even forget to set the torpedo for slowest speed,so it can actually reach its target.
The further out you are (in my opinion) the speed setting is the most important torpedo setting,and I think it would be wise to even set the torpedo a knot or two faster (target speed).
For me mag torps can be very useful from the rear as I mentioned,and also when not able to get into optimal position,and any angle will have to do,yet at the moment I am still able to get into good positions,have'nt met ships faster than me yet,other than alerted warships.
Mag torps may also be better for very large ships,like battleships,as you would want to cause massive damage very quickly,for fear of some serious retaliation.