Great info!
I'm also a VFD. Wife and I burn brush once or twice per year. The piles are 10' high and 20' diameter. People who handle lots of brush know that it compresses when you pile it up. Our brush piles are also from what we gather from spring cleaning/pruning.
What I do. To prevent fire from spreading we burn between summer showers. A weather front blowing through can mean disaster. Add one quart of diesel to the middle of the pile. I then devised a tool for giving the fire some help. I take an almost empty 5 gallon propane tank with a regulator. Place the fuel supply inside (copper tube) a 5-7' long 1" pipe. Place that 1" pipe inside (not threaded) of a 20' long 2" pipe. I use aluminum pipe because its light and easy to manuver. This gives you plenty of distance for safety reasons. Sometimes placing a support (old bucket) in the middle is necessary to support the long pipe. Allow the end of the 20' pipe to rest on the bottom of the burn pile. Now comes the fun part. Have a small fire (usually burning paper) at the end of the large pipe. Turn on the propane,,,just a tad at first. When it catches turn it up a little more. The diesel should be ignited by now. After 3-5 minutes, even starting with a wet pile every thing should be well on its way to burning. Turn off propane valve and place tank 1,000,000,000 feet from fire. When you turn off the propane you will get a small "backfire" from where the pipes connect. That happens within 3-5 seconds. Not loud or anything, its just a poof sound.
If the fire is stubborn to get going but has developed some hot spots, crank up a gasoline leaf blower. Without the hotspots the blower is no good.
On a safety note, Keep the gasoline away from a fire. Remember, gasoline is NOT flammable, but those vapors will kill you.