Siphonic, gravity-powered toilets are provided that include a toilet bowl assembly having a toilet bowl. The toilet bowl has a rim channel provided along an upper periphery thereof and a direct-fed jet channel that allows fluid, such as water, to flow from the inlet of the toilet bowl assembly to the direct-fed jet outlet port into the interior of the toilet bowl, in the sump of the bowl. The rim channel includes at least one rim channel outlet port. In the toilets herein, the cross-sectional areas of the toilet bowl assembly inlet, the inlet port to the rim channel, and the outlet port to the direct-fed jet channel are configured so as to be optimized to provide greatly improved hydraulic function at low flush volumes (no greater than about 6.0 liters per flush). The hydraulic function is improved in terms of bulk removal of waste and cleansing of the bowl.