I don't understand all your terminology, but some of your assumptions appear to be mistaken. Terminology- "max allowable helicopter nose (pitch up)", relative to what? "3ton helicopter"? which I guess means an aircraft 0f less than 6,000 lbs?
I can't help you with Agusta 119 or Bell 429, but I have lots of experience with the AS350 and variants, no Bell 407 but tons in the earlier 206 that it is based on.
First, I can't remember a light airframe in which the CG moves aft with fuel burn, with the limited exception of the 206 Long Ranger in certain situations, the exception is limited and I'll talk about in a bit.
The AS350 fuel tank sits beneath the main rotor and aft of the allowable CG envelope except at very light loads, and even then the fuel load is in the aft envelope. Besides the fuel tank, the only loadable area that can move the CG aft is the aft baggage compartment, which has limited capacity. You can load this type such that you exceed the aft envelope limit, but it hasn't happened to me more than a couple times in 30 years on type when the aft compartment had an unusually heavy load snuck into it. The nose came up unusually into a fully controllable hover, no danger to of a tail strike. In fact, the few times I've busted the CG envelope, the aircraft was absolutely controllable in normal powered flight. And that's the trap, you lose an engine or are otherwise required to use an unusual amount of control in one or more axis, and you're a test pilot because now you may not be able to control the aircraft normally.
With the fuel aft, burning fuel moves the CG forward, typical in light helicopters. The exception is the Long Ranger, and I think the 407, which have 2 smaller tanks under the middle cabin seats. They fill at a midrange and burn at the midrange, so while the saddle tanks are being depleted the CG does move aft. The fuel burn is from the top of the main (behind and under the rear seats) moving the CG forward, then the middle/saddle tanks are emptied, moving the CG aft, and then the remaining main tank fuel is consumed. That was 25 years ago, so check your RFM...
What seems to happen as the aircraft burns fuel is that one can often increase paylod, especially if the CG envelope expands forward like the AS350 does. It's not unusual for me to leave base in my HEMS configured AS350B2 with a patient weight limit of 250 lbs for CG, and then have 350-400 lbs cg limit on the stretcher weight.