Thanks Gav. In this instance the two channels were kept and applied separately. I have and do produce a blend of Lum and Ha using PixelMath, setting the output for greyscale, but it all depends on the target and the contributions of the two channels, as you'd expect. Ha can sometimes create havoc with delicate blue reflection nebula and one goal was to retain the RGB combined blue in and around the Ghost.
Much appreciated Steve - your Esprit 150 would make a lovely Ghost (if you haven't imaged it already). A four panel mosaic or larger is still an undertaking even when you have a greater frequency of clear skies; planning when to collect Ha, when to collect the Blues etc is all important if you are aiming to stretch your technique.