What combinations of filtration are you using? What enlarger do you have? Most colorheads are calibrated in density values (for example 0-100 giving 0.00 to 1.00 density equivalent for the three colors Yellow, Magenta, Cyan). And some don't even go up that high.
Multigrade paper needs the magenta to go way over 1.00 - so to get into the higher values you may need supplemental filtration, probably only need a single (1.00 density magenta) filter in a filter drawer or under the lens - then use the dial to fine-tune the results.