I don't go out to San Jose until Friday, so I can't say anything definitvely. However, though you are correct that being side mounted is not the best position, I really believe that Frank honestly didn't care. (If I am corrected on it this weekend, I will report back). IMO, Frank feels he is dominate enough in ANY position that he will just let it go there and he will win.
If you remember Frank's first win in the UFC against Kevin Jackson, Frank didn't resist at all the takedown attempt by an Olympic gold medal wrestler. He then went on to submit him with an armbar within seconds. Frank's general game plan (and the way we train) is to be extremely good in all areas, then wait for the other guy to make a mistake (or we keep up a dynamic enough presure to force one) and then take advantage of it.
I could be wrong (and will report back honestly if I was), but I really believe that Frank was as happy as a pig in mud to be where he was. If he could have KO'ed Renzo Gracie with strikes from a standing position (like he did Cesar), it would have been less work and a quicker victory. OTOH, I know that with the length of the fight, I would have been quite comfortable in the bottom of a side mount if I were able to land kness. I would have felt that I was getting the better of the exchange and was wearing him down, because that is something that we train extensively. Also, Renzo doesn't have much muscle density in his back to absorb those knees. If I were Frank, I would have thought I was in the better position.
Let me state this clearly, IMO (I did not talk to him about this specifically before this bout, but I have heard him voice this type of opinion before) going into the fight Frank was confident that whether it was stand up or ground, striking or grappling, that he had a signifcant edge. I know he had (though if my assessment is wrong, this may have changed) no fears of a pure ground submission contest with ANY of the Gracies. Over the years, he's been more of the mindset of proving that his strategies and methods were not only more versitile, but superior in every respect. I believe that if Renzo had not tried to get away from the knee strikes by exposing his head and neck in a north/south position, Frank would have gone on to prove just that.