What fitting is this?

You are correct about that for the most part. The reasons behind that are MC volume for the front port is smaller, and presence of a residual valve. I removed the residual valve because I don't have drum brakes. I had to choose which end got the larger volume. Either way one set of disc brakes was going to have a smaller MC volume. In a daily driver application this is a problem because as pads wear down the fluid level decreases. I'll just be sure to keep an eye on it. I won't be driving it too much anyhow. Maybe when I swap MC to larger piston I'll try to find an equal volume unit.