Advice with Activation Groups and Stored Procedure Programmes

We have  server programmes (Java)  that use JDBC which in turn runs the
QZDASOINIT job in order the access data in our I Series.  External
Stored Procedure (RPG COBOL ...) programs are a means used to access the
data base. We have recently had problems  which we have overcome by
changing the activation group of certain external stored procedures form
*CALLER to *NEW, but we would like to understand why this overcame the
problem. 

I have 3 questions

Does anybody have any advice as to how we should be defining our
activation groups with external stored procedure programmes ?

Does the QZDASOINIT job open all external stored procedures in the
default activation group ?

External stored procedure programs are usually written using SQL
(Result Set) Are there any caveats as regards activation groups and
stored procedures. We have the impression that SQL executes in an
activation group apart from the host external stored procedure program.
?

 

Many thanks for any help that you can give.

 

Paul Papworth