Actually, I tested both autoswitch and foreswitch, but some results are not expected. For instance, I set autoswitch on US Aerial. If I change scale to 1:1128, the background displays 'Map Data Not Yet Available' even though the eMapSwitch tab shows it is on US Aerial (the default basemap). I have to click the US Aerial again and then the autoswitch functions well (to the right basemap I set).
When I play Zoom-out, it always displays US Shaded Relief (not the default, neither autoswitch nor foreswitch) even though the eMapSwitch tab shows it is on US Aerial.
My suspection is that loading Shaded Relief from the server could take shorter time than loading US Aerial probably due to the loading size issue. This is only my guess.