AT two inches wide and one-third of an inch tall, a display ad shown on a smartphone isn’t much of a canvas for a creative marketer seeking to promote a product or service.

That’s one reason smartphones are not working well as a medium for many advertisers. The evidence is telling: advertisers are willing to pay much more to reach a thousand pairs of eyes gazing upon a computer or tablet than a thousand pairs looking at a smartphone screen.

“Size absolutely does matter,” says Christine Chen, director of communication strategy at Goodby Silverstein & Partners, an ad agency in San Francisco. “If you look at the real estate available on a smartphone, it’s really sad compared to not just banner ads on the Web, but also to TV, print and outdoor advertising.”

Size isn’t the only problem. Advertisers are also limited by what they can find out about smartphone users. It’s not technically possible to use cookies with smartphone apps the way it is with a browser. On the Web, publishers typically record users’ actions so that advertisers can make an educated guess about a user’s identity and interests.