I'm going to jump in here because I think there's potential for confusion in the questions/answers recently posted. The common rule of thumb about trailer loading
is that there should be a 60/40 split of the overall weight of the trailer + load that places 60% of the total weight (trailer plus load) ahead of the axle.
The original M416 design places the axle very close to the center of the tub, and if you put weight evenly in the tub (let's say you split 100 lbs. of load evenly between the front and back of the tub), the result will still be slightly biased in favor of the tongue because of the weight of the tongue, even though the axle is an inch or so behind the center of the tub.
If you use the tongue for cargo, as shown in the photo of my Dinoot m-series prototype below, you can achieve well over 60/40 weight bias with an axle that's centered under the tub, even without any cargo in the tub. In the photo below, I've got two jerry cans plus mounts (full weight about 40 lbs each), a cargo box (weight of box = negligible), but say I put 50-lbs. of gear in there, then add in the weight of the tongue/coupler/jack, etc. and you've got maybe 175-200 lbs. ahead of the axle that isn't matched behind the axle.
So depending on how you plan to use/load your trailer and what gear you plan to carry on the tongue, a 50/50 placement of the axle under the tub is very appropriate.