Ask yourself first if you really need to develop the negative to N+2 instead of using some other means to get the extra contrast you need such as using a higher paper grade, selenium toning the negative, switching from a diffuse light source to a condenser one, etc. I have found that grain and tonality are better with some combination of N+1 and the above things. When all else fails, I bleach and redevelop in a staining developer to give me more contrast. I rarely develop more than N+1 anymore.
FWIW, when I was testing some Kodak films years ago, I found that higher dilutions enabled me to get more contrast. I ended up using a 1+63 dilution (a bit more dilute than dilution E... but not that much). Maybe you can try that. Do make sure you aren't exhausting the developer before you reach the contrast you want by testing once with more developer than you need.
Best,
Doremus