Steam heat system mixing

I have a two pipe steam heating system, however a bathroom was added using a one pipe radiator. This radiator has a bottom connection versus a top connection like all the other radiators. The one pipe radiator has low heat and only keeps the bathroom temperature at about 59 degrees in the winter. I tried adding the largest size vent valve, tipping the radiator, and inspecting for clogs with no luck. My next idea was to increase the size of the piping as only ¾ inch copper is used to feed the steam. Could the low heat problem be caused by having one pipe and two pipe radiators on the same system?