Wood ashes also collect in the small chamber in the basement under the chimney. As a child in Michigan, one of my hamsters escaped his confinement. Poor little Pinky couldn't be found in the house, but a couple of days after disappearing my Mom found him in the chamber covered in ashes that had cushioned his fall. (He made a full recovery from his adventure.)

I think if you're having to worry about makeup air cooling the house down than your fireplace heats it, that's less to do with chimney placement and more with how the fireplace is designed. I.e a gas flame in a fireplace with no appreciable thermal mass and a chimney that pipes the heat straight out is where I'd look to first as a problem.

A massive stone fireplace that's heated with a single load of fuel, then has its chimney flaps closed to keep the heat from escaping, is going to be much more efficient. I wonder if maybe the fireplaces in many parts of the USA are actually designed to not heat the house too much, given the usual weather in e.g. Texas.