The knee looks good. But i have a touch of advice. At the bottom front of the knees. i'd suggest you round off that angle there. then if you go around the bottom edge of the knee with a heat gun and bend in the foamex inwards to create a bevel on the edge. it can really make a pair of simple knees look great.

The orange here indicates where to heat and the red shows which direction to bevel the edge. Hopefully that makes my explanation clearer.
I create the bevel by putting on some thick gloves and pinching the sintra at the edge and bending it inwards.
I use the same method on my thigh plates, cod, the top of my shins and the sides of my back plate behind my shoulder blades. it is particularly useful on the back plate as it removes or lessens the crease that often appears in that spot, which is caused by the lack of compound curve where the horizontal curve of the bottom of the back meets the vertical curve that starts mid back and goes up over the shoulder. this creates a slight compound curve, but a lot of the time it doesn't create quite enough to fully remove the issue.
Sorry that got a bit longer than i intended it to but hopefully the info is useful. If you check the photos I'm tagged in by Cassandra on facebook you can see one of my back plates in better detail.