What else do you have on hand for a developer?
I only ask because I am not familiar with Agfa developers.
...however, I can say that your "minute a stop" thing should not be used. That is more of a color approach to overdevelopment, where all varieties of film are designed to run in the same process for the same time. If anything, a percentage is better as a rule of thumb. For instance, 140% for +1 and 200% for +2.
You must also realize that you underexposed your film by two stops, and that pushing only seriously affects your mids and highs.
Additionally, while Fuji's Website lists it as an "ISO" 1600 film, nowhere on the data sheet for the film does it state "ISO" 1600. It calls the film "EI" 1600. This means, that they keep you in the dark as to what the true ISO is (unlike Ilford and Kodak, who plainly state that their magic films are actually ISO 1000 films). Since they only list development times up to 3200, my guesses are 1. Fuji is being conservative, and only lists a one stop push over the ISO in order to prevent unrealistic expectations. 2. The film is actually an ISO 800 film, and possibly lower. 3. In either of these cases, perhaps Fuji refuses to either test for or publish times for extreme underexposure, as do Ilford and Kodak. Ilford lists a lot of times for higher EIs. 6400 is on their chart in several developers, and even 12,500 on there in a few developers, I believe. Kodak even has info on exposing the film at 25,000.
If the latter is the case, your film is actually three stops under or more. You had better hope that your reflected metering was actually telling you to overexpose your shots in this case, as reflected meters can easily do in the dark. Or you can hope that you get some shots that will work well being very dark and without a lot of detail...which may very well be the case. I love a lot of shots like that, and many of my own are made that way on purpose; even exaggerated toward that in printing at times.
You should also realize that sometimes an underexposed negative is actually easier to print if it is not overdeveloped. In a contrasty situation especially, this is the case.