Good morning Allan,
One point that comes to mind that I have done for years on beams, before starting the flange cut, pre-heat the center of the flange at the web junction considerably. I generally do so from both sides to make sure it is really warm. I also pre-heat the entire cut of the flange running the torch up and down it a couple of times usually from the 'back' side (opposite the side I will be cutting from). This makes it easier to make a very nice, clean, smooth cut. Then, don't use too large of a tip. Bigger is NOT better. Use the correct size tip for the thickness material you are on and the correct oxygen pressure. Again, more is not better. Unless you are on very heavy beams, over 2", 40 lbs is enough.
One more thing, as I cut through at the flange to web junction I give the torch a slight inclination toward the drop piece. I can deal with the tab that is left better than the slice into my good part.
He Is In Control, Have a Great Day, Brent