I've never fretted over a couple of tablespoons of residual yeast. Obviously you were left with more than that. I'd like to hear from more brewers who have had this problem. It's one that keeps cropping up yet is one I've never had. Using an upside down carboy was a compromise over the ideal shape for the kind of fermentation system we were shooting for.
Carboys are relatively easy to find and are made of glass which are easy to clean and sterilize.
Designing a cap to fit carboys, therefore, was the difference between just having an idea and having an idea you could share with everyone else. The shoulders of the carboy do tend to collect sediment more than we would have liked, thus the sharp twisting back and forth action that Ken wrote about. But when done regularly, and that means from day one, we always found it to do the trick. As for hop pellets, don't be lulled into thinking they're nothing but powder. Upon rehydration, pellets can be found to contain whole leaves which would have a real impact on the way the BrewCap operates, especially when it comes to draining away the sediment.