To this day, I still find people not agreeing/not understanding the finer points of auxiliary arcs, especially on Vassal. They report certain features of the arc graphics as bugs, but this isn't the case - it's how they're defined. This is a mini-series of posts where you must understand the first level of enlightment before you can agree to read the next level. You may ask for clarification in a level before accepting the facts and passing through the next level.

LEVEL 1:

Fact: aux arcs have no overlapping area to the front arc

consequence: there's a sharp discontinuity in range when checking both the front arc and the aux arcs at their transition

The center of the range 1 circle colored in cyan is at the corner of the ship. This could be physically drawn with a compass. It's often (not always) the best starting point for many best-line calculations for aux shots. The red line is the arc edge that acts as the frontier between the left aux arc and the front arc. Here, it acts a restriction that must be obeyed by all lines for an left auxiliary arc shot, ie, an aux arc shot can't be along a line that crosses this edge. Lastly, the cyan line is a radius of the cyan circle.

When comparing these two lines:

1) from the corner of the ship to the circle's intersection to the arc line, in cyan

2) from the aux arc/front arc frontier point to the circle's intersection to the arc line, along the red line

You arrive at 2 different ranges. The Aux arc shot will be range 1, because the cyan line is shorter than the one along the red segment, so lowest-range = best kept range

The in-front-arc shot will be range 2, because you can't even consider the cyan line here, you must take the one along the red segment, so you're stuck with range 2.

when you are ready, go on to level2:

https://community.fantasyflightgames.com/topic/262804-psa-auxiliary-arc-path-of-enlightment-part-2/