It boils down to having too much laser for fine details: an 80W laser cannot produce the small amount of power required for those lines. The tube cannot fire at very low power levels, somewhere around 10%, so reducing the Min power much further will likely prevent it from firing at all.
In addition, the laser head will not reach the 300 mm/s you expect, because it cannot accelerate fast enough. The charring in the corners shows what happens at the slowest speeds, with the middle of the lines being somewhat better. The much longer lines along the roof show good results at higher speeds.
You may get better results by converting the vector details into a filled layer and engraving them, because the laser can then travel at the commanded speed across the entire front of the pattern.
An earlier discussion about creating small brick patterns explored similar issues: