Imagine some lines of braille text. Single out one or two characters. Draw straight lines around the chosen characters at the nearest points in the surrounding braille characters, left and right, above and below. The rectangle shows the amount of exclusive space a braille character needs. Distance to the lines above or below is about 4mm, to the left or right 3mm, diagonal 5mm. In Autocad I've developed small boxes, to be inserted in the drawing, showing the amount of exclusive space needed for 1-7 characters, see appendix Autocad.
Take care with initial or final characters that do without a complete row or column of braille dots, like character l or the capital sign: despite the open space the same area should be cleared as around a full character.