In my case, I used frames with the dimensions 30 x 40 cm (approx.
700 g with the glass).
So, a 10 mm total height of the individual magnet towers is ideal, since the back of the frame is usually a little bit set back towards the glass.
Also, the number and strength of the magnets is more than sufficient.
However, since I have parquet floors beneath the pictures, I wanted to be overly cautious.
To change the pictures in the frames or to totally remove them, quickly peel them off the fuse box.
This way, the magnets remain in their positions on the metal sheet, so you can reattach them again easily.