I am curious if anything has changed or what you have done about this...
I also fly Ag in an OH-58 and a 206B3... The OH-58 I fly is actually very stable with regards to the N2 fluctuations, although I have cyclic issues that make it a little wild at times...
I don't have as much time in the 206B3 but the one thing I did notice right away while flying it a little is that the N2 runs all over the place compared to our 58. Just like you said, I set my N2 just at the redline or a hair below and try to leave it there as much as possible. When I am lowering power I get a rise on the N2 that goes up to about 102%, but I am gentle with it because I feel like if I get too aggressive its going to spike a lot more... when I come back and land I find that the N2 still gets sucked down quite a bit and sometimes out of the green... Nr is within green but I still get a little nervous when I see that N2 droop so much... It does come back, but 3-5 seconds seems like an eternity while I am waiting for it. Our mech says is no big deal and that I need to just let the gov do its thing...
anyway I am just curious if you have come too grips with it or if you have figured out something that might be going on to cause the fluctuatuions...
on a side not, how big are the loads your taking off the truck and what kind of torque you pulling? I am curious cause I feel like I am pulling the guts out of the thing everytime I come off the truck...as carefully as I can lol