Bed Extender fit with Racks?

I'm looking to replace my bed extender that somehow walked away from me a few years ago. Seems I'm finding much more use for one these days. However, for about half the year I have a set of Thule XSporter racks on my '05 DC TRD that I use for kayaking.
My truck already has the factory QR mounts for the extender. So, my question is, can I fit one of the OEM or Amp extenders in under the rack posts since they overhang the rails by about 4 inches? I noticed that Amp now offers a "Sport" version made to fit with rail accessories and a "Max" version that utilizes more of the bed.
I'd rather have the Max and flipping the extender over to the inside shouldn't be necessary since the QRs should allow me to remove/replace from any angle right? So, I need to know how much vertical clearance is needed to get the extender under the racks. How much inside the rails does the extender sit and how high on the sides? Anyone have experience with this or willing to take a measuring tape out to their truck for me? I would appreciate it.

truckbed by JLeePhoto, on Flickr