You need to understand the way a skimmer works in order to fully understand why smaller skimmers don't really do much.
A skimmer pulls organics from the tank by getting them to adhere to the micro bubbles it creates. There are a few factors involved in efficient skimming, but some of the more important ones are bubble size, bubble count, and contact time.
Smaller bubbles more easily adhere to organics, and in large quantities, provide the surface area to do it well. However, in order for them to work effectively, the bubbles need as much time as possible in the water column. The time allows them to pick up as much gunk as possible on their way to the collection cup.
Most smaller skimmers can get a lot of tiny bubbles, but because of their size, can't get much contact time. Manufacturers have tried whirlwinds, long tubes, bubble plates, but it still comes down to physical size.
That said... I would consider ditching the Whisper, and getting a good HOB.
