I have made Tren E with 2% BA and 15% BB @ 125mg/ml.... I didn't have any problem at ALL with it staying in solution... Been over two months and still as good as new...
If you want to go higher, I would suggest adding 20% BB at least... Also, just to thin the mix out a little, you might want to add 20% anyway.. I mean, BB is not the most expensive thing in the world