@Vu -- unfortunately I'm not allowed to provide you a test page.
Upon further investigation, I'm seeing that the window in which the iFrame with loader12.html is rendered has innerHeight/innerWidth of 0, which is the reason that's 0x0 is being sent to initAd().
Interestingly, in insecure VPAID mode, the same thing does not happen -- initAd is sent the correct dimensions. However, I need to use secure (ENABLED) for other reasons.
I can confirm that I'm doing everything consistently to the examples you linked to. I can also confirm that correct values are sent to adsManager's init().
Any speculation would be much appreciated.