Is their any intention behind these sentences when the writer puts "however" into different places? or is it just a whimsical way? Could someone explain to me about this mtstery?

A)However, my uncle refuses to quit smoking.
B) My uncle, however, refuses to quit smoking.
C) My uncle refuses to quit smoking, however.

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There is a different area for stress, aka emphasis, in each sentence.
A) However, (pause of emphasis) my uncle refuses to quit.
for context, I would use this when saying "he was a life long smoker, and recently found out he has lung cancer. the doctor told him to stop smoking; however, my uncle refuses to quit."

B) "My uncle" is emphasized. (My grandmother finally quit smoking for her health. My uncle, however, refuses to quit.)

C) This again places emphasis on however, as well as smoking. (For his health, my uncle quit drinking. He refuses to quit smoking, however.)