BA: I think 5% is a reasonable maximum, and 2% is a nicer figure.
BB: Up to 20%.
How much BA to use and how much BB to use are mostly independent issues. The importance is how much of each rather than how they relate to each other.
The only respect in which there is importance there is that since both are solubilizers, in some instances reducing one might require increasing the other, if wishing to keep the same mg/mL value.
For example if one had been used to using 5% BA and 10% BB at some particular mg/mL value and that value was really pushing it, then a decision to reduce the BA to 2% would require increasing the BB.
Along the general theme of the thread, the simplest Fina method is to use 38 mL of suitable oil for each 2 g of trenbolone acetate (whether powder or a cart of pellets that nominally contains this amount); sonicate in a jewelry sonicator until all is dissolved; or in the case of pellets there is only sludge remaining and no visible remnants of pellets; allow to settle; and filter.
In the case of powder the sonication is not necessary. Heating in a warm bath to example 55 C (use an insulin syringe through the septum with the plunger removed, so as to allow heated and expanded air to escape) or simply with quite hot but not boiling water will allow easy dissolution of the powder by swirling. One may have to return to the swirling from time to time as the process may not be immediate.
The sonicator is not actually necessary for the pellets either but much more patience is required with the pellets.
The above formula gives 50 mg/mL.
Usage of 2% BA / 20% BB allows at least 75 mg/mL, but if using the pellets the filter may be gummed up rapidly as a result of including the cosolvents.
The same general method above can be followed with other materials and adapted according to desired mg/mL.