1. I would try the ankle DF movement with the foot/leg unweighted, like up on a chair or box.  If some of your weight is on the leading leg, that could cause you to reflexively tighten a little/lot to support your weight and balance.   try that – do you get more ROM when unweighted?

2. have you tried distracting the ankle along the length of the leg? you anchor a band and wrap the other end around your ankle. lay down in the direction away from the pull of the band with the band pulling your leg away from the hip. you can use a low support like foam roller to rest your calf on.  this helps create space in your ankle bones.  do this on each side and then retest the ankle DF unweighted. do you have more ROM?

3. i do not know what your manual therapist can do, but a good chiro/PT/sports med person will be able to release your ankles, similar to a chiro releasing your vertebrae.  if you find one to do that for you, test the ankle DF ROM before and after he does the release. is it better?

4. do any of the above mobs mentioned in this thread work better than others? it can be very time limiting to work all around your leg.  test/retest after each one and focus on the ones that have the greatest effect.  do you have any tightness that is lingering/always there in your lower leg? that would give you a clue also.