A medical probe includes a shaft for insertion into a cavity of a patient body, and a distal-end assembly. The distal-end assembly is coupled to a distal end of the shaft and includes a hollow tube having (i) a first opening, located at a first section along a longitudinal axis of the hollow tube, and having a first size that limits bending of the first section by a first local radius of curvature (LROC), and (ii) a second opening, located at a second different section along the longitudinal axis of the hollow tube, and having a second different size that limits bending of the second section by a second different LROC.