I'm 6' with, as the bike fitter told me, "gargantuan femurs".... That said, knickers can be problematic. I've never found an off-the-shelf knicker that does fit as you describe, just below the knee. Some do cut into the back of the knee, but others don't. It depends upon the fabric and the cut.
My best bet for shorts, knickers and tights has been boure (boure.com). While I have them make custom shorts for me (about 4" longer than their standard short), I have yet to pay up and do the same for knickers. They're knickers don't seem to cause me problems even though the knee articulation is about 2" above my knee. Other brands have chafed at the back of the knee. In the end, it all becomes trial and error I'm afraid.
2009 Waterford RS-14 S&S Couplers - Brooks B68-Anatomica - Traveller
2008 Waterford RS-33 - Brooks B68-Anatomica - Go Fast
2012 Waterford Commuter - Brooks B68-Anatomica - 3.5-Season/Commuter
2011 Surly Troll - Brooks B68 Imperial - Snow Beast