So I sorted out the mobile display issue by trail and error - the fix was NOT to use the file copy / merged file copy of includes/templates/your_template/common/tpl_main_page.php - by reinstating the original 1.5.7b file set version, i.e. unmodified, the middle box appears correctly and the mobile version also appears as it should. This worked for me, I am not suggesting it is a fix for everyone, just reporting my fix.

I have not yet tried to set middleboxes for pages other than home page and maybe the plugin file version of that template which contains code for middleboxes 8 & 9 may be required for those positions to work - at the end of the day the home page was my main requirement.

Thanks to mc12345678 and balihr for the assistance I have received.

cheers,
Mike