Reply To: Main Content + Sidebar in iPad portrait view.

Try this CSS code:

@media screen and (max-width:840px){
   #container #main #content {width: 65%;}
   #container #main .sidebar {width: 35%;}
}

@media screen and (max-width:480px){
   #container #main #content,
   #container #main .sidebar {width: 100%;}
}

Replace 65% and 35% with what value you set on Frontier Options -> Layout
You can also change the value 840px and 480px to your desired screen size for tablet and mobile.