窶堋オ窶堋ゥ窶堋オツ、like 窶堙??堙?, is used at the beginning of the sentence to elaborate a contrasting statement or stipulation ("but," "however," etc)
all of the variations of 窶堋ッ窶堙 are identical in their meaning, and used at the end of a clause, usually before a comma and second clause. My understanding of the different cases to use them is dependant upon the context, and is more a matter of the rhythm of the sentence than a grammatical difference.