Sorry for the late response!
I feel like having 5ml of fluid allows a little room for error and is easier (for me) to get the dosage more accurate in the syringe. I find it easier to draw .5 ml and get rid of air bubbles or whatever without losing any product.
Also, having 5ml of HCG mix...
Put 1ml of bac water into the small HCG vial. Gently swirl the vial until the HCG is mixed. Draw the 1ml of reconstituted HCG into a syringe and inject into a sterile empty 10 ml vial. Add 4 ml of bac water, swirl gently.
.5 ml will be 500 iu of HCG. This is what I do….