The V that you see is only at expiry (like any hockey stick) and completely independent of vol or tenor. All that matter is notional. Assuming put backspread, you sell a put with higher strike, and buy it back with lower strike(same maturity). The more you buy the steeper.
Vol will only impact the position of V. The more expensive the long positions are, the ...
How do you define higher payoff? Could you show what you compute? Do you look at what the options cost at the moment?
If you want the same payoff (graphically and expiry), you can do the two things:
buy call (say ATM) and sell call (OTM)
buy put (ATM) & sell Put (ITM with same strike as OTM call)
Now, it is intuitive that (although same strike and ...