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Making burnt ends out of tri-tip is like using prime rib to make beef soup, both are very good, but not the best use of the cut you have available. Hot tub the tri-tip, no more than 130ºF and then power sear it, either with cast iron or directly over lava hot coals. Using a brisket rub or something like Montreal Steak Spice and some butter, slice it thin (across the grain of the two distinct muscles) and the burnt ends may have some real competition.
Sure it works - the suggestion to go legs up is to get the flames to wrap the setter and save the gasket. With the setter in the legs down position the lump is so hot the flames will always be directed right at the gasket.