VST, by their own admission, operate in the “value” end of the Cigarette market. That is why there is a difference in margins. I absolutely agree with Dinesh that there is very little overlap between their products. One of the factors could be that British American Tobacco has large stake in VST as well as ITC.
In regards to Cigarette volumes I have attempted to do a deep dive on this and have posted in ITC thread which is linked below
I used this information for a DCF model that I was making for VST Ind.