I'm playing that scenario as Septimus. What i understand until now is that NM influences only max coehsion for each unit and cohesion recovery speed. Impact on coehsion recovery is a simple consequence of having an higher MAXIMUM cohesion. If you don't boost also coehsion recovery then increasing only the MAX cohesion value transform this bonus in a malus because a lot of calculations, excpecially in battle, are influeced by the ration Current Cohesion / Max Coehsion. So, the main bonus i see with higher NM is boost to max cohesion value.
Due to the fact that cohesion losses in game are not in % but are fixed values (for fixed i mean not depending from the max value but still variable in a range), an higher max coehsion is useful to:
- minimize impact of coehsion spent in attacking (very minimal)
- minimize impact cohesion loss suffered under attack (medium)
- minimize impact of cohesion losses due to movements. In other words, your unit is more (a lot ? few? i dunno) mobile and can move relatively far without reaching in exausted mode a region where it will fight.
When i say "minimize" i means that the percentage
Current cohesion / Max Cohesion goes down slower than enemy one but still goes down.
The main matter is that who conquers Rome is very near to the treshold of 170NM that states the end of match. Who conquers Rome has to continue to fight and battle until the end in order to deserve his conquest so this treshold should be increased.
At the same time who conquers Rome automatically has to fight against 2 enemies in 2 quite far theaters (you got "the treaaaasure, my treaaasure", now all want your treasure with all their forces), plus internal ones that sometimes force you to deploy entire legions in theaters not interested in the main fights. This means that the key factor for him is the MOBILITY without sacrifing a lot combat readiness. Making Italy your fortress is a no-no because you will permit to your enemies to assault you in force and maybe together. You need to continue to mantain initiative, on both fronts.
Anyway I still don't played a lot this scenario, those above are thinking of a newbie, so i can't say what should be the right NM bonus. Maybe +75 is to much, expecially for factions that start with NM higher than 90 but at the same time +25NM could be not enough to survive to the wolfpack assault.