Hey @omad1 forgive me if you already are utilizing this method with Sovrn.
While we do not have a responsive unit like Adsense, we DO have responsive capabilities. Utilizing an ad server (DFP) makes this process the most efficient for not only the publisher, but the publisher advocate (ex. me).
Ex. Adsense Responsive Leaderboard ATF
-Assume this unit can display as a 728 x 90, 468 x 60, 320 x 50, 970 x 90
Sovrn's method for this example means you must create 4 tags/creatives in Meridian, then make one line item for "Sovrn Responsive Unit ATF" and choose the above 4 listed ad sizes. You would then upload the Sovrn tags/creatives within DFP.