To be clear re. walking at IAD during OP's connection, one would need to walk from the arrival gate towards C1/C2 to get the escalators down to the CBP facility, through the facility including TSA, from the TSA exit near C7/C8 to the PL at C17/C18, and then finally from the PL to the departure gate of IAD-FLL (which could be as far away as D32). Still beats EWR though IMO.