Hi Lawrie. Yes, I came to the same conclusion when figuring out how the Bahtinov mask works. Have a look at http://www.btinternet.com/~gfcarey/bahtinov.htm
and scroll down a little to see my 'Y' diffraction pattern. The Y mask would indeed work, but of course the Bahtinov with many parallel slits produces a much brighter diffraction pattern.
After I had figured out the Bahtinov I realised that my 6" reflector has a built in mask due to it having 3 spider vanes!