I cooked up some frozen chicken breasts from a wire grate on the bottom of the cookwell with thermostat set to around 375 and the chicken cooked up perfectly within approx. an ~hour +/-.
However when I cooked a chicken mix it must have taken over 2 - 3 hours to cook. I added 3 cups water and milk, the pasta and spices which your suppose to bring to a boil and allow to simmer for 12 mins.
However it actually took a long amount of time where there was some simmering in the bottom of the 18 quart cookwell after a couple of hours. The chicken pasta and mix with approx. 3 cup of liquid would only low simmer and not produce a rapid boil Eventually cooked up well but took a long time because temperatures in the bottom of the cookwell stay low at around 150 deg. F with temperatures at the top of the cookwell around 300 deg F. This is with the thermostat set to 450.
I think when only around an ~inch of liquid on the bottom cookwell isn't high enough to reach the hot areas from the cookwell sides, perhaps requires to be another inch or two higher.
I think the frozen chicken breasts did ok as hot air produced higher in the cookwell was able to permeate the chicken found from the rack at the bottom.
I don't think a roaster oven is able to adequately boil liquid when there is only around of inch or so from the bottom.
Liquid usually requires direct contact from a cooking vessel to bring to a boil within several mins. (approx. same time required to boil water, etc.)