I’m utilizing the option for “responsive” ads when I put DFP together manually but I think there is an issue with your plugin. In your options you set that you can specify multiple ad sizes for a single slot. So I put this in for a leaderboard: 728×90, 300×100 – Basically its a desktop leaderboard and a mobile leaderboard. When I load my page it only shows the 300×100.
According to DFP instructions to serve different sizes for different mediums you simply have to define ‘size mapping’ like so: defineSizeMapping(mapping).addService(googletag.pubads()); and then specify in the ad block: gptAdSlots[0] = googletag.defineSlot(‘/1032425/NJM_728_home’, [[728, 90], [300, 100]], ‘div-gpt-ad-1437068224697-0’).
And then you specify the size of the screen and what ad to show when you’re at the screen size.
addSize([320, 400], [300, 100]).
I suspect that your plugin doesn’t allow for such an option and that is the reason why my 300×100 is showing instead of my 728×90?