HD Multicam with 4k clips

I have 3 4k videos I'm wanting to do an HD multicam with. I want to be able to "Punch in" the 4k footage on the HD Multicam timeline. It doesn't maintain the 4 k footage in the hd multicam timeline. I choose Fit to Frame. The footage normally goes to 50 percent, however, it stays at 100 percent. I changed it to 50 percent, it just shrinks the footage to half the frame. I do this often but this time it just isn't working. Please help!