With sound, it is, if not impossible, at least very hard. With that high bearing spread your estimation is useless, unless you draw least and most possible area of probable courses. If you want to use 4 bearing method, maybe use periscope instead of sound, when possible. Bearings will be far more precise.
But in my opinion the best way (at least when escorts have no radar yet) is to overtake convoy while nearly outside visual range and use 0 bearing method (described in other topics) - simply you cross convoy's course while taking bearings at regular times and at max visual range - intersecting bearing lines taken while approaching with observed course lets you also know speed.
When you can't get within visual range, at least try by trial and error method to steer such a lead angle and speed that all contacts stay in the same bearing and closing - that means you are on a collision course which lets you approach a convoy.
Ausdampfverfahren method can also be then utilised.
Read here
http://tvre.org/en/acquiring-torpedo-firing-data