A factor you may wish to consider is Dry Down. Some papers do not require this consideration and I don't know if yours is one of them. But a print will dry to a darker tone overall than is anticipated when looking at the wet print. IF your paper is subject to dry down and you haven't taken that into consideration then you will get an even darker print after toning. This is not to say the blacks will lose seperation but they will not look well defined.
Les McLean has a lot of info on dry down in his book and there probably is a lot here if you do a search.