Myth: header bidding always lifts revenue

Myth: header bidding always lifts revenue
The pitch: "add more SSPs, watch RPM climb." Diminishing returns are real. RPM lift by partner count, n=85 sites, 28d:

— 3 SSPs baseline
— 5 SSPs +11% ▮▮▮▮▮▮
— 8 SSPs +14% ▮▮▮▮▮▮▮
— 12 SSPs +13% ▮▮▮▮▮▮▮

Past ~7 partners, lift flattens while auction latency adds 180-400ms, dragging viewability and Core Web Vitals. Net was negative for 3 sites above 10 SSPs.

So what: cap demand partners near 6-7, prune low-win-rate bidders quarterly. ▲0% past partner #8.