If your technique is not working. It is never ukes fault. Look more closely at your technique and find out why.
If he is able to reverse you then you must have left an opening. Find it and close it.
Cherie is so correct. I think this is worth repeating.
Regarding the OP:
1. Have you ever thought of calling your 8th Dan Sensei over during these interchanges to show the best way of dealing with this situation?
2. As said before - without kuzushi there is no Aikido. As a Judo man you should know this. In Judo no waza is effective if kuzushi is not established and maintained throughout the execution of the waza. The same goes for Aikido - the only difference is the use of tegatana as the primary point of contact and the ma ai is different. Check your technique, are you establishing kuzushi? Are you maintaining it throughout or is it being lost somewhere?
3. I would take this person as a gift in training. By being larger and a bit difficult he is challenging you to perform at a higher level than you have been able to muster so far. If you have sound principles then his resistance should help your technique not hinder it (hence option1 above - that is a litmus test). If your body structure is not aligned with and supporting your point of contact with your partner it will be very difficult to generate kuzushi, movement or anything else.
If principles are sound static or moving does not really matter.
Use the opportunity to be even better than before.