I'm going through the same thing right now. I just bought an Eagle Ciras in a size small (I'm 5'7", 150 lbs). I'm looking for BALCS-cut soft armor for it too. From what I've been able to find, the vest size is based on the BALCS armor size (i.e. small CIRAS requires small BALCS, medium CIRUS requires medium BALCS, etc.). This only seems to apply to vests designed to accept BALCS-cut armor (Eagle CIRUS, Paraclete RAV, FSBE, SPEAR carriers). The tricky thing is that any size of these vests will accept small, medium, or large hard plates. On top of all this, most places only want to sell BALCS-cut inserts to LEO/MIL (which is a load of sh*t) and they want around $1000/per set (nice, huh?). Anyway, that's how the sizing works. Let me know if you come across any size small BALCS that are available to us civies and won't cost my right nut.