ball heads pointing straight up

As mentioned in first reply, yes.

Here's an image from a freezing test...

You can see, just how large the panoclamp is. The fastening knob is here turned downwards and will not in this postion allow the ballhead housing to rotate freely on its base, but turn the knob pointing upwards, and all is good to go. Then it can actually turn to ~95-100 degree vertical...

To give you an idea of the possible problem with the mentioned low-profile ballhead, have a look at this review: http://www.scvphotoideas.com/2012/05/sunwayfoto-xb-44-low-profile-ball-head.html

If I used my panoclamp on the Sunwayfoto ballhead, a vertical position would be impossible.

Hope that helps,

Jan.