Unfortunately the front axle is where it must be when figuring moments. If you have not had the luxury of lifting too much in the bucket and have had the rear end lift up while on a side hill, then you will know the fright that develops. pivoting on that front axle.. The tractor then pivots around down hill. Try it some time and that rear axle statement will change in a hurry.
On the other hand, yes the rear axle is only the fulcrum if you load so much in the rear box that the front axle comes off the ground, then yes you also have the problem, but I surely doubt that that has ever happened to any one with such a ballast box.
While you are adding up the contributions to the resisting moment around the front axle, I didn't list all those other things that contribute, each according to its weight and distance from the front axle, all measured in foot ponds. They are, in part, the transmission, the engine, the hood, even the arms of the bucket behind the axle.
Those that run loaders without a ballast box or other rear weight, but with or without fluid in tires get by, but any extra farther back weight of course gives more ability to do some heavy work with the bucket. I don't have a ballast box, but a heavy blade back there does pretty good for me. On one tractor, I have done very heavy bucket work with rear tire fluid plus about 500 pounds of steel hanging inside each rear wheel rim. No rear blade or ballast. Great rear traction also. Tractor was blue 28 HP.
In summary, You want your resisting foot-pounds moment to be much larger than the bucket and its load moment of foot-pounds. How you get it is up to you, but measure from the proper place, not the rear axle.
Sorry about that "moment" word, but being an old civil engineer, I can't help but use proper terms and proper static analysis.
,, carry every thing in the buck LOW but Im sure you already know that
