BERLIN — German weblets are taking a larger slice of the ad pie. Over the last three years, large commercial webs RTL, SAT1 and Pro7 have lost up to 5% of their ad market share to Germany’s smaller channels, Hamburg-based trade Media Facts reported in its most recent edition.Together, Germany’s weblets claimed 19.3% of TV ad revenues in 1996. Ad income of the larger networks rose, but at a lower rate than at smaller channels such as Vox, RTL2 and Kabel1. Overall, private webs attracted 89% of TV ad revenues in Germany last year. Yet Media Facts analysts claim that some of the territory’s TV stations may be in trouble: Commercial channels in Germany took in a net total of $3.9 billion (6.56 billion marks) in 1996, but intense competition and spiraling prices led them to spend $4.5 billion (7.6 billion marks) on programming.