So I dug up my old spreadsheet. I use it to figure axle and tongue weights when I haul round bales of hay since the numbers can get out of hand fast.
Either way, this is set up for a 30 ft gooseneck trailer and should be similar in response to most trailers we pull since they are normally 25-35 ft.
I took all the bales off and simply modified the weight of the bale on the back. It's going to be close.
No load on back, tongue = 1400
200 on back, tongue = 1345
400 on back, tongue = 1290
Theoretically proves that for x amount of weight you add to the rear, it takes 25% of that off the front. My guess was close.
On the axles, it appears that you will be adding approx 63% of the weight you add to each axle. This equals more than 100% if you add the two, but that is due to the cantilever.
I hope all that makes sense and is helpful. It is all theoretical and every inch of axle placement will modify the actual numbers.....but it will be dang close.