I thought that what I’m missing is a better brush. Turns out, what I was missing is a better magnifying glass.
There are magnifying glasses for 10-15GBP, with names like NZQXJXZ. I went for a 30GBP magnifying glass instead. It worked, but I didn’t like the shadows.
Now I got myself a magnifying glass from Brightech. Twice as expensive, 70GBP, but what a difference it makes. There are no reflections, and no shadows whatsoever. I immediatelly noticed mistakes I made with the previous glass just a couple of days ago, and fixed them using exactly the same brushes.