There are 2 major muscles in the calf. Your explanation, unless slightly modified will address only one of them. During the calf stretch, if you lock your knee and drop your heel, the gastrocnemius is stretched. This stretch sensation may extend to slightly above and behind the knee, as that is the insertion point of the gastrocs. The soleus will be stretched only when the knee is bent as the heel is lowered, taking the gastrocs out of the stretch. Try it and you will see what I mean. It's a small but very important difference.