He qhimm, I know that you have done the most work with the Field Script commands, you said that most are guesses, you mind sharing what you have?
1) I want to flesh out what I have in Gears.
2) I don't want to do duplicate work.
I don't trace though field script backend code, but change the values of the parameters while the script is still running in an emulator (PSX) This tends to give me a little more data about the command quickly.
Of course, you could always just disassemble "JUMPMAP", as that's field file loader. You can at least see what data goes where and get a difinitive format of the field files.