The position of an adverbial word or phrase

Hello, teachers!
Please help me with these sentences.
1. I met my old friend by accident in a bookstore.
2. I accidently met my old friend in a bookstore.
3. I met my old friend accidently in a bookstore.
I think #1 & #2 are natural, and #3 is somewhat uncommon. Am I right?

Then what about these?
4. I broke the vase by accident.
5. I accidently broke the vase.
6. I broke the vase accidently.
I guess #5 is the most common and #6 is ok, but #4 is somewhat unnatural. Am I right?

Thank you very much.
Best Regards.
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