Well, wave 3's channel, and that's what you illustrated on that chart quite well. The BTK could be in the C of 4 down off the 514 high. 50% of the A down would be 458, which is the area of the 20-EMA on your chart:
If that's the case, the BTK might make a double top at 512 on the next leg up, or a fib above that. 458 is also an important level for the BTK, so that's another reason for it to be support on this leg down.