Non-90deg mitered bends
I wasn't able to track down an equation, but the Transmission Line Design Handbook (Wadell, 1991) (sec.5.5.3) contains a table of optimal arbitrary angle miters for microstrip width to height ratios and bend angles. Here's a table giving the values (taken from here):



and here's the bend diagram and corresponding equation, taken from Wadell:



\$M=\frac{x}{d}\$

You can use bilinear interpolation to estimate the optimal miter for other width-height ratios between 0.5 and 2 and angles between 0 and 120 degrees. For example, this gives an optimal miter for the OP case of 19%, which corresponds to the measured image dimensions.

Unfortunately, I don't know of a way to calculate miters for width-height ratios outside this range. Still, hopefully this can be a useful starting point for a proper EM simulation.