Most will attest to disliking combination brews. Aside from their novelty factor, they are very impracticle for real world use.
On a side note, you'll find plenty or recipes for high mg single esters here! Simply make each hormone to its max dilution, then combine in a syringe when ready to use. This way you can control the amount of each.

Its less of a recipe, and more of simple math. We need to know how to cancel units here, and thats IT. Heres some helpful (and brutally simple) equations and constants to remember:

mg/ml x ml = mg

1g powder = 0.8ml (realistically its anywhere between .7-.85 but more usually 0.8 for long ester liquid stuff)

We know we want 10ml of 200mg/ml test mixed with 300mg/ml EQ (500mg/ml combo). 2/20 ba/bb ratio.

mg/ml x ml = mg
200mg/ml x 10ml = 2g test
300mg/ml x 10ml = 3g EQ
Total powder = 5g
Total volume = 10ml
(-) 5g x 0.8 = 4ml (powder volume)
(-) 10ml x 0.02 = 0.2ml (BA volume)
(-) 10ml x 0.20 = 2.0ml (BB volume)
Oil volume = (10 - 4 - 0.2 - 2)ml = 3.8ml

Mix, heat, stir, clear, fliter, enjoy.