Well, it sounds like you know him very well and are doing just what he needs to help him settle. It also sounds like he is only mantra-crying (the whinges), doing what you are doing, sitting by him and helping when needed sounds perfect for him learning to self settle. One thing you might try, depending if you feel it might be worth a shot, is to leave him to do the self soothing on his own, some LOs are bothered by mummy staying in the room too long. Mine was. There was a fine line between him wanting me because he had teething pain or something and not wanting me because he wanted to be asleep so I was to go out of the room, that was quite hard for me to be honest and there was a certain phase where his mantra cry sounded very sad but he was not full on crying, I felt I should stay with him but he did not want me there it just put him off sleeping. So I told him "I'll go so you can sleep, call if you need me" and leave, I stood outside the room with a clock to see just how short the mantra cry really was, like 1 minute and he was asleep. Through this phase he also sometimes let out a loud but very brief cry right at the need of his mantra and half a second before nodding off - all very confusing for me as I wanted to dash back in there to him but he was actually fine and if I held back outside the room for those few moments (I must make it clear, this was not CC in any way, he was not calling me or properly crying) past his brief loud cry-out and then sneak in I saw him sleeping very peacefully.
I will also say, Tracy said it takes 20 mins for a LO to fall to sleep and for some it is the full 20 mins of the mantra cry before they nod off. When mine was a new born he did take 20 mins to fall to sleep, later though I learned that if his mantra went on for more than say 5 mins this meant he would not be able to settle alone and needed a quick help. I'd listen on the monitor and if it got past about 5 mins I just popped back in and put a hand on him, told him everything was ok and either stay a few mins or leave again depending how I assessed his reaction.
If your LO has a lovey it can be a huge help in self settling, perhaps introduce one if you haven't already. At over 6 months I think it's ok to leave something like a small stuffed toy or muslin in with them for comfort but if you are not happy to leave it there you can let him self settle with it then pop in to remove it a few mins after he falls to sleep.