From your photo; the trailer is pretty close to level.
Placing the nose of the trailer below level won't help, and may create new instability issues.
You could gain an inch of additional height by changing the spring shackles for longer ones.
Drop hitches come in two inch increments, so changing to a straight bar may put you too low.
In the end, an inch too high or too low should not cause instability.
If it is already on the edge, it might help, but correcting the real problem is a better direction to take.
If it is still unstable, I would bet money that the axle is too far forward.
Adding weight to the front may still help, but if not, adding length to the tongue will, in effect, push the axle further back.
We are all talking about adding weight to the front, which is good, but is there weight behind the axle that can be removed?
Rob