nothing was changed on the engine modeling since "forever" - in fact not even with the advent of XP11, as we calculate thrust in our own module. N1 required to taxi depends on weight, slope and temperature - values in excess of 40% seem excessive, though! Judging from the V2 set up you must have had a pretty high grossweight, though. As a matter of fact, to have a V2 of 162 the plane would need to weigh about 70tons...
The engine´s acceleration depends on the engine "age" - which is randomly set between sessions. We did this because real engines rarely accelerate equally well and also show slightly different parameters (EGT, N2, ...) for the same N1.