In a nutshelll then I think we can all agree that the best strategy is just stick to trying to slip through and make as much distance between yourself and the convoy as you can.I normally evade on a 90 degree course from the convoy's previous course,evade DCs for approx 1 hr using whatever methods I can at that moment,slowly come to PD with no ballast,have a quick scan around,then surface if all is clear.Or,I would just wait until I am in my predetermined radar clearance zone,and begin my next 'catch up' phase of the attack.I will never be bullied from a convoy into breaking off my attack,i'll keep at em until I run out of torps or have sustained significant damage,or am being harrassed too frequently by aircraft at the same time.
I just thought how thrilling it would actually be to follow
under the convoy,then surprise them with your next attack from within
Cheers for the answers anyhow.