Unless you have a lot of detailed information and the math ability of a professor, experimentation and observation is really the only way(weigh?) to determine the effects .
Your trailer is not an exact balance scale .
Variables include such things as number of axles and their placement fore and aft. Oddly, tongue attitude has a greater than expected effect on tongue weight.
You might start by weighing
the tongue at the right attitude then adding a known weight to the back (such as a family member or a stack of concrete blocks), then observe the tongue weight again.
That might give you a reasonably accurate ratio to work with.
Within reason and capacity, more tongue tongue weight is better than less and a slight down attitude is better than an up.
On tandem axles, level is more important than on singles to accomplish evenly shared weight on both. But for tongue weight,as you lower the tongue you concentrate more weight on the front axle and also shift the balance point forward at the risk of overloading the axle.
Now I am getting confused !!
What was my point?? OH yeah! It was that observation works better than calculation for those with limited information or limited abilities to interpret it.!
Anyway.... My front rack has worked well for me but you must still be aware of tongue weight and the possible need to balance your load, and/or enjoy the effects of increased tongue weight where tolerable.
The good news is that RV trailers once set up and balanced tend to stay balanced, unlike utility trailers.
Hey! how about a rack on each end made from light
weight material, then you can distribute the bikes front and rear for balance?