When soldering, you should always flick the heat on to the pipe so it gets heated up as well as the fitting. You are correct with holding the heat to the end of the junction between the pipe and the fitting because it will pull the solder in, but you should also start applying the solder to the bottom of the joint. When you start on the top, you are lucky if you get half of the joint filled with solder in the bottom half. If you start applying the solder in the bottom, with the heat applied at the end of the pipe inside of the fitting, you will then pull the solder full depth into the joint. Then you can go around the sides as needed, then finish on the top. Also, make sure the pipe is not a sealed system without some type of faucet or valve being open to allow the steam to escape from the system when soldering,,, not an issue here, but certainly could be in a real world scenario. These thoughts are from a Journeyman Plumber, and I think you have the right idea, but a little recommendation from here,,, I will say that the only solder joints I have ever had leaked when I was an apprentice were because I started soldering from the top of the joint and not the bottom. I was concerned you were not going to wipe the excess flux before soldering, but you absolutely did and I have to give you credit! Overall your skills are pretty good
I clean the access flux after I've applied heat for a bit, I can clean up more of it ensuring no runs. I also don't drag the solder around the joint, it gets too messy for me. If it's a horizontal like the bottom joint of that 90 I just run the solder around the crown and watch it flow around and down till it leaves the buld on bottom then knock it off with my finger tip. If it's a vertical I tap the joint in one spot with the tip of the solder (preferably the back, opposite of heat and where no one will see it) and let the solder flow around until its filled. Lastly, when the fitting is still hot I wipe it down all over with the flux brush _then_ wipe the flux off with a towel. That way there is no discoloration from heat or staining from burnt flux. Longer process but to me the perfect swet joint is one where it looks like someone drew a small line around the joint with a fine point silver marker. I know, I'm weird. 😒
