OK, I finally got it - Thanks to Pablo once again.
It seems however that the tool that I can control better the layout - is Layout grid, not FlexBox
So here is the final page : http://www.beleuramyhome.org.au/page1.html
What I have here is the following : One Layout grid in th emiddle with 2 columns
The left column has in it an iFrame with two different height settings, one for PC or a Tablet, the other one shorter for Mobile phone.
In the Right column of that Layout grid - I inserted a FlexBox with Zero pedding, zero margins and the setup is
Row, nowarp, flex-start, flex-start, center
Inside it I plugged my Blog Object with Flexbox setting of 1,1,30%, center
That final setup of the Blog object achieves a proper view for bot a tablet in portrait and lanscape as welll as for mobile phone in portrait. In mobile phone landscape, it works but doesn't look fantastic... But I can't have it all...
Now, to the next challenge
Thanks again Pablo