As with so many cultural things in any country, there are some big no-no's that you have to avoid 100%, but there are also a lot of grey areas. Due to China being a huge country and every part of it being in a different stage of development, socially, financially, industrially etc, it is normal that you will see all kinds of behavior. And people are in general more flexible accepting different behaviors because of that. So while you might search for the perfect rule, it will really depend where you are in China, whom you are having dinner with and how expensive the restaurant is.
In this specific aspect there is a cultural clash between the rural Chinese style where a dirty table means that the food was so good that you could not help from eating messy and the (perceived) European fine dining style where everything is neat and clean and no spot on the table or elsewhere. This is quite similar to the way Japanese noodles are eaten: One indicates how delicious they are by eating them boiling hot and compensating that by loudly pulling in air along to cool them down.
So here just some observations that I made over the last 10 years:
What I realized is that for a lot of Chinese food it's really hard to keep the table cloth clean and not really expected either. So if the table cloth gets dirty because its virtually impossible to get 30cm long noodles out of a high bowl using chopsticks or even with a large spoon or because you drop your bones on them, does not make too much of a difference (for the table).
It's normal and necessary to spit out the bones (as you described it, dropping them) in China and Hong Kong. There is simply too much food (specially chicken and fish) with tiny bones in them, since they cook the chicken in whole, chop it with the bones and serve bit-sized pieces with the bones still on the meat. You cannot help but put the meat with the bones into your mouth, chew off the meat and then try to get rid of the bone. While this is not very common in Europe and people usually try to cut the meat off the bone before eating it, and then even hiding the bones somehow, this is not the case in China. A big plate of empty bones is rather a sign of a good dinner since the best meat is considered to be right on the bone, and the fact that the food is served with the bones is a sign of freshness.
Regarding where to drop the bones:
A classic Chinese food table set consists of a main small plate, a small bowl on another small plate, a tea cup and chopsticks. Since soup & rice dishes (which are easiest to eat from the bowl) and other dishes are often served in parallel, your plates are quickly used up. If you want to reserve one for the bones, you are in trouble. So where else to put them?
In better restaurants they will simply change your plate often enough so that you can drop them on the main plate. Waiters come around and change the plates if they see a lot of bones or when you ask them for it. If this kind of service is not there, it's normal to drop them in a small pile next to the plate. It's simply something you have to do otherwise there is no space.
If you feel uncomfortable doing this, you can use the small bowl for the bones or take the plate below the bowl and use it for the bones. But then the soup running down the side of the soup bowl will make a spot on the table. If you want to be neat, take a paper tissue (it's always a good idea to bring some to a Chinese dinner) put it on the table and drop the bones on it. When you are finished with the food, pick it up and put it on the plate before it's taken away. Problem solved.