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I'll start with how it used to be. For each chunk, it will try to place 3 fossils but it will only happen if the conditions are right. It will get a random X and Z coordinate within that chunk and a random Y coordinate within 20 - 50. If the block at those coordinates is a gravel block it gets replaced with a fossil block.
Now with the update, it will try to place 4 fossils per chunk instead of 3. I haven't been fossil hunting in the new version yet but I don't think the generation rate increase would be very noticeable although it is helpful. It's still largely luck based so all you have to do is keep trying (but I know how frustrating it can get). Hope you guys find some soon!
There are no magic levels in that range that spawn more, it is completely random. I personally have only found 2 fossils ever while digging. They are still very rare, but it is better than it was in 2.2.