Hi, I just test the code below:
<amp-ad width="750" height="429"
(BTW it took me a lot of time to get that characters <> in your examples at the beginning and the end command data-zone and data-access-code are inproper ;-) )
Back to the point...Does it necessary to specific width and height for the ad? In non AMP ads/zone/placement there is only a maximum size for the ad required, and its works fine becouse, as I noticed this ads can resize depending on device.
With an AMP code, when I put the same size of ad, on mobile it apears to biger than screen.
I'm not sure if I made my self clear. Hope you get what I mean. If note I try to make a screen shot