hmmmmm let's just simplify it... the vol curve moves, the spread between 1m and 9m moves... If front end vol looks expensive, I can sell it. Whether I sell 10 lots of the 50 deltas hedged with futures or sell 20 lots of the 25 deltas hedged with futures depends on the skew but i will be short vega regardless of the package... on the contrary, I can buy back end if I am looking to be long vol over a longer term period. again, how i structure the package depends on the skew ( how much of a difference are the wings vs the meat) then you have a synthetic time spread
Many thanks to balls and Sle on this post and all the other contributors. I think I have the information I need now. Very much appreciated and thanks for the great feedback!