Lower the amount of water. Beersmith may advice starting with 2 qts/lb. However, in decoction mashing, boiling water is infused to hit rest temps if temps weren't reached by the decoction or for rest temp maintenance. The added water plus dough in water might total to 2 qts/lb. If you have a fired mash tun it's not as much of a problem hitting or maintaining temps. The decoctions need to be thick heavy mash except for mash out, when mostly mash liquid is pulled. Enzymes are better preserved in a thick mash. I start with 1 qt/lb. If the grinder puts a cloud of dust in the air, I'll up the amount of water slightly. The only time I add extra water is to thin the decoction mash to hasten conversion or in the mash tun to do the same thing. I use a fired mash tun. If I'm a few degrees low, no problem. It takes less fuel to reach a rest temp than to boil water for infusions. For a 28 lb grain bill, I use 4 gallons of thick mash to go from acid rest temp of 100F to protein rest of 125F. I'll vary the amount pulled depending on whether I do a one temp or a two temp conversion rest in the mash tun. Don't scorch the mash during decoction boil. Pay attention to mash pH when boiling the mash. Boil the mash in the decoction kettle to get the mash to shoot out small geysers of liquid. The boil needs to be strong. The mash should be boiling across the entire surface. What you experienced, happens. Do a bunch of tri-decoctions and you'll learn how much mash needs to be pulled for rest temps. Stick with it, it takes time to gain experience.