Thanks for all these comments and thoughts. I kind of understand why I got stuck and surprised to be kicked off the campaign (saying major defeat !) after the second scenario whilst being able to reach the two western approach victory locations ... and only getting a minor victory condition.
The map conversion from ASL is superbe but the play is a little frustrating. I wonder if there are other scenarios in this campaign or if it has only two. Too frustrating to replay the whole thing to see - though I liked very much the 'short' duration of those scenarios (only takes half a day to play each when take time, as I love to do, to watch the action replay from different angles after each turn ... though even the smallest scenario takes ages for me to complete )