Yes I think the flux scorching comes from the lower heating power. If I remember right, flux is only active during a certain amount of time until it saturates with oxides. Since with air-mapp you have to heat for a longer time to get at temperature...

EPP, I was also reluctant to use compressed oxy-acet gases. Based on the experience of BF member Papa, my setup is with a medical oxygen concentrator and a BBQ propane tank. Works well so far. A bit safer from not having compressed oxy.