Don't forget that the std. rule of thumb for utility/flat bed/cargo/larger camp trailers will be quite a bit different from a TD or tiny trailer depending on the layout.
The typical TD has most of the weight and heavier cargo items located in the galley, which is typically in the rear, so the balance point is typically further back than other trailers where cargo is typically spread more evenly, or even biased toward the front. Typically.
Also, side door placement for the "sit and spin" method of entry and requisite clearance for the fender location may also dictate, to a certain degree, where the axle goes. So what has worked for even an experienced trailer builder may not be ideal for a TD style camper.
The std. rule of thumb for TD's is more like 38 to 40 percent of the cabin length referenced from the rear of the cabin. Some vintage TD's even have the axle set much further back.
Using my 9.75 ft long cabin as an example, if I use paintm4u's method I get an axle location of 48.75 inches forward of the rear end {((9.75 ft x 12 in/ft)/2) + 9.75 in = 48.75 in}. Whereas using the 40 percent rule I get 46.8inches {9.75 ft x 0.40 x 12 in/ft = 46.8 in}. At 38 percent its more like 44.5 in.
Where you stow your battery, cooler, CI pots and skillet, camp chairs, side tables, ez-up, etc. will probably have the biggest effect on preferred axle location, but the fender and side door relationship will usually dictate how far forward the axle can physically be.