Just re-read the DIY link and checked out their website. The key word in the Heating section is "preheat" -- they only heat the pipe (initially) to start the overall heating process, then move to the fitting to fire for effect, as it were. Keep in mind that the objective is to get the entire joint slightly above the melting point of the solder, while not getting any part of the joint too hot -- which would destroy the flux and oxidize the pipe and/or fitting. At that point all you can do is take things apart, re-clean, and start over.
If you concentrate most heating time on the fitting, and tap the end of the solder wire on the pipe next to the joint, you will notice the solder first just taps and feels like solid wire, then it feels a little soft or dull, then it sticks as it melts but immediately cools, FINALLY it flows into the joint.
Practice makes better.