This is incorrect, especially for solar farms
Panels are indeed only about 1/3 of the cost. Additional components, labour, inverter, mounting - another 1/3.
The last third is indeed soft(ish) cost, but this includes profit (duh..), certification, survey, tax, fees, etc. This can be reduced, but it is not going to magically disappear ...
Another fun fact : newer mega farms in low-altitude deserts are considering no-axis no-mounting zero-tilt - just laying the panels on the ground ... It all comes down to cost vs yield
A nice project by the way. Did you ever compare the results to pre-calculated angles based on time/location/season?