Lots of stuff to consider, and, I'm not sure that I am interpreting the situation perfectly well. But, I'll toss this out there, as, at one time, in my mind, I had a similar feeling (but, without the knee pain -- and who knows if it really was similar to what you are experiencing). In fact, when I had that feeling, I usually cranked out more power and was faster. So, one consideration is to raise your seat a bit or get the seat back a bit, or something to lengthen your leg. At least play around and see if that floating feeling -- assuming it is not a good thing -- abates when you adjust your position to lengthen your leg (or with any other adjustment).

I, perhaps too often, am in search of the perfect fit. I try to get to a state where I am all set. And, as a result I fiddle. I try a little of this, which leads to trying a little of that. And, this can be a function of my conditioning and flexibility throughout the year. My sense is that you should do some fiddling around and see what comes of it.