On my tandem axle trailer the lower I go with the tongue the lighter the tongue becomes. The higher I go the heavier. Shift in balance point between the axles. I've had enclosed tandem axle cargo trailers, when empty, the tongue would never touch the ground.It's 1 percent for 6 inches, on my trailer. So, about a thousand times as much as you think.
But it's important to understand that the amount of load on the tongue is not the issue. The issue is the center of mass position. If the C of M position is already marginal, then even a small shift aftward can be significant. It's a stability problem, and stability is notoriously non linear.
Disagree on the tongue weight not being an issue. I could put 5000# (227kg to you) of lead right in the center of a tandem axle trailer with no tongue weight and the thing would wag just due to tire and suspension deflection.