Dark stock proportions When making croquettes, I always end up with more meat than I can use. That is to say that I'm aiming at about 20% meat in a flavor-full concentrated velouté.

The problem I'm having is that I use about 400gr meat for 1 liter of water, and that's 40% meat to begin with... (OK, after cooking the meat loses 50% weight, but I have no idea how much water evaporates).

I'm afraid to use less meat, but maybe I could add more bones?

What proportions are appropriate for a nice dark stock (or an ordinary one)?
According to the Culinary Institute of America their basic formula for all Meat or Poutlry based stock would be:

8 lb/3.63 kg bones and trimmings
5 -6 qt/4.80 - 5.76 L water
1 lb/ 454 g Standard or White Mirepoix

You would not need any actual cut of meat for a stock according to them.  Those would be reserved for making a broth.  Their basic formula for broth doesn't specify a ratio between meat and bones just 10 lb. of meat or poultry including bones to 5 qt water.  If you are converting a stock into a broth they give the formula of 3 lbs meat to 5 qt stock.  Based on that a good starting point might be 7 lb bones and 3 lb meat to 5 qt water.

Just an FYI they make all their mother sauces using stocks, broth seem to be reserved for soups and other applications.