Negatives for Carbon

I'm using lampblack powder. I started with 12g per liter and didn't get much relief (well, it's there if you look for it, but it's nothing spectacular). I'll try to halve that and see how it works.
So far I've tried some negatives of "normal" contrast (for silver halide paper) and needed to go as low as 0.75% dichromate to get decent contrast, so I guess the pigment concentration was low enough already. Next time I'll try some negatives made for vandyke so I can get away with less pigment.
Thanks.

Vlad it really is a balance and what is going on in the image. I have some images that I think will not print very well some times. I've gotten good relief with 16gram tissue and the dichromate right. What is also important is the proper exposure to get deep into the tissue. Again I say it is a balance of all the factors which makes it fun. After a while it all starts to come together and printing gets real fun.