You CAN exceed 81.5ly with normal movement under certain circumstances. Your example however appears to show that the intercept routine puts a hard limit on 81.5ly for non gravitronic ships. It would be interesting to test if you move a ship 81.4ly into a warp well and intercept it with a ship at the same location, does the interceptor wind up on planet or outside the warp well. If outside the warp well, the hard limit on intercept could actually be 81 light years.
Normal_x = rnd(warp^2/(way_x^2 + way_y^2) * way_x) - .5
Normal_y = rnd(warp^2/(way_x^2 + way_y^2) * way_y) - .5
Also, I use the tanascuis tool mostly for quick glance at ship costs for any races with any loadout and also when cloning where I simply double the megacredits. It does however have a movement function where you can input xy coordinates, warp and mass and predict the exact spot you will end up next turn. The Nu interface sometimes reports information that doesn't correspond exactly with what will happen that turn, and I call them quirks (like pba NOT being a PBP code despite the interface highlight coloring them like true pbp codes) rather then actual bug