PJB, you got the point!
Seems that the DSRV release and approaching works fine if made with the sending and target subs one in front of the other, and not from the rear of the target sub.
We did some tests and I confirm that sending the DSRV from the front of target sub avoid the crash against the conning tower: tomorrow night we will play the scenario and I will post the result.
Thanks for help and suggestion.