ABL and Geo 13 are the combination I use as well, but the recipe I have followed uses a 2:1 ratio. For 2 gallons of milk (plus another pint of added cream), I use 1/32 tsp of PC-ABL and 1/64 tsp of Geo 13. Seems to work well ... but I doubt it would be much different if I used, say, 1/16 tsp of PC with 1/64 tsp of Geo.
Is this your first batch of brie, or similar cheese (camembert, etc.)? If so, get ready to become addicted ... I never cared much for brie or camembert until I made my own. Oh, my -- beyond delicious. Can't wait to see your results!