Well not all the cure is going into the meat if your brining it the way you did. I would assume you are actually quite low in overall ppm.
The point of the matter is, you should follow the manufactures instructions. If they say 1 tsp in a brine of 3 qt water then that is what you should be using. Quite possibly their cure salt recipe could be of a higher nitrite level not needing as much as the other brand.
I'm going to do what they call a "combination cure". What this means is I'm going to do and injectable and then apply a dry rub then let it sit for about a week or so under refrigeration then wash it off. I will take my cure to lb. ratio according to the manufactures directions and divide it in half. One of these will go into the rub, the other into the injectable.
When I inject flavorings I put all the spices into a large coffee cup, add about 1/3 water and heat. Let her boil a few times then for a few minutes between then pour the mixture into an old reusable coffee filter that I sit in a measuring cup. I use the back of a spoon to remove the excess water from the spices and then discard the spice. Then let it cool back down tell nice and warm and add my cure and stir a few times until it's dissolved and inject.
