The baskets are a bit of a compromise size in order to fit 18-26 grills. They "fit" best in a 22 and deliver the kind of controllable heat "most" cookups need there. Only one will fit in an 18 without seriously cramping your cooking space, and with two in a 26 you might not have enough heat for some things.
I'm not saying the baskets won't produce good results in a 26, just noting that the machine does use more fuel.