some hcg gets trapped in the neck of the vial- so if you're mixing really concentrated, you're wasting more hcg. plus if you tried to mix in the tiny vial you'd be drawing out such small amounts that it would be very difficult to measure out an accurate dose.

most docs mix for a volume of .2cc's per shot. some people feel it's absorbed better if it's slightly more dilute, but i don't think there is any research to back that up. although in general, hormone shots are designed to be given IM because the hormone can get "trapped" in subq fat (that's why estrogen shots are always given IM)- so having it a bit more dilute certainly can not hurt. i think more than .5 per shot is totally unnecessary, and once you get up to 1 cc it can be a bit overwhelming for the subq tissues. i generally mix to a concentration of .3, .4 or .5.