I can't say that i have read all the posts in the forum as i don't have that much time but I'll just chip in my thoughts on this. I apologize if this overlaps with other ppl's advice.
I have encountered similiar problems especially when i want to bring the guy to the mat in the irimi motion. I've seen other variations which don't describe such a wide arc and keeps uke close to the body without going so low but it's always a pleasure to bring the person down but the problem arises when you either can't turn the guy/bring him down or you'll end up scrambling over the place as you have mentioned earlier.
With your problem of throwing the guy down effortlessly, I would think it would imply that either your irimi motion didn't put him off balance enough or that as u said ur throw may be wrong. I've been told by my sensei that there are two main ways of doing this. The first one would be a straightforward take down which would be cupping the chin or lower face bringing it up(using his getting up momentum) and then describing a circle to the mat. This was the first one taught to me but i found it difficult to deal with those that didn't really seem to want to get up or if he was getting up too slow. The other one is getting the head kinda in between your arms and slightly above ur lower ribs(you know like those wrestling chokes). Then u just move ur whole body forward as if walking in one swift motion and the guy should lose balance and fall down. The low position of the head is meant to make sure the guy can't get a proper stand. Trust me it works, this guy did it to me like 6 times in a row until i was totally convinced. He didn't even throw me i just kinda tripped and lost balance. I wonder if this was the 'inside the shoulder' throw u were talking about.
Now with the turning motion this is tough to explain but never rush it or just stop it. It is tough to get as in my opinion it needs a good deal of centralization. The key is slow practice to get ur technique right making sure that your your balance is there at every moment so when it is speeded up your legs would be firmly rooted to the ground and you won't go spinning off. I find that it is one of the techniques that seem to allow a bent hand(which is the one holding the neck). I hate to use the word ki but that's the only way i can explain it, extension to the ground and in a circle and the guy will have to follow.
If it helps, the guy's attack must be sufficiently committed so there would be a momentum to utilise. Slow practice would not give you the same feel and there's a high chance he will successfully resist but it is necessary to get the right technique especially if u feel u're spinning off before you attempt full speed.
Imagine this a guy coming with you with a half hearted strike or you intercept his strike then stop and then move into the irimi motion, you would be using your own strength to turn. However if he attacks hard and fast there would be his forward momentum to utilise. So don't worry if he doesn't go down or turn. It will all come in time. Oh and when you turn, it's good to look behind you as it helps visualize the turning motion.
And of course there's the timing in which to enter and come into contact with the body which needs to be so that u get him just as his attack subsides but he still has forward momentum. No stopping. You are right in thinking that there is something wrong if it feels icky.
So that's my piece
Good luck!
