From my experience, the only way to figure out how much mg/ml can hold is by doing small sample (1g) brews and see what works.
The strategy is to start a brew with a low concentration (mg/ml). If that works, increase the mg/ml by adding more powder the same brew, and see if that works. And keep going like that until it cannot hold anymore.
Example: Test P
Start at ......... end at
50mg/ml ==> 75mg/ml
75mg/ml ==> 100mg/ml
100mg/ml ==> 125mg/ml
... etc., etc.
If you're brewing multiple compounds together in the same brew (aka "blends" or "mix"), use the same idea, but only change the concentration of one compound at a time.
Example: Test C + Test P
Test C 200mg/ml
Test P: ___ mg/ml
Start at ......... end at
50mg/ml ==> 75mg/ml
75mg/ml ==> 100mg/ml
100mg/ml ==> 125mg/ml
... etc., etc.
I'm not sure I understood your question; are you asking what you should look at when determining the mg/ml of a compound?
If this is your question, then you should look at the compound's melting point. More often than not, when a compound has a lower melting point (melt easier), it will be able to hold at higher mg/ml.
For example, Boldenone melts easily at room temperature and looks like a thick oil. When it comes to Boldenone's mg/ml, it can be made at 600-800mg/ml or even higher.