in my experience, knee touching the calf is bad. it implies some kind of pressure of your knee into your calf, so it's biased weight. if you have to move from that position, you have to counteract that weight first.
of course, there's the possibility that you ever-so-lightly touch your knee on your calf, but dealing with that precision in a quick sparring situation seems pointless.
a note to YMAA practitioners, Unicorn Stance is the one where the knee is behind the heel; it is more forward and backward. Cross-Leg Stance, the back leg is more to the side, as in crab-walking or side-kicks. we usually also say knee 1-2 inches from the ground. it makes for better training
of course in a real situation, it would be higher. but when you're training, train lower.
Nicholas C. Yang
President, YMAA International
Assistant Director, YMAA Retreat Center
http://ymaa-retreatcenter.org