[chimerax-users] How probe radius should affect exposed surface area?

Hi, I am trying to measure the exposed surface area of lysine residues in DNaseI (4AWN). I am using the "measure sasa" command. To my surprise, when I am increasing the probe radius (1.4 A, 5 A, 10 A etc.) I receive larger exposed surface area. Is that OK? Many thanks, Alon