Currently have SRAM Red 10sp gruppo on my tri bike, with the tri shifters of course. I swap my wheels between my 11sp road bike and 10sp tri bike and am tired of changing cassettes. So, I already have an 11sp wheel and cassette of course. And an 11sp chain.

I've heard that perhaps I only really need an 11sp rear shifter as the 10sp rear derailleur can be made to work since the magic of how much cable is pulled happens at the shifter, but not sure if this is true. Can anyone confirm?