Axisymmetric oscillation frequencies calculated for different β and NSs with j = 0.2 and two particular values of q/j²: q/j² = 1.5 (extreme NS compactness) and q/j² = 10 (high NS oblateness). Left: Radial mode. Right: Vertical mode. The curves indicating particular values of β are normalised to the maximum value, β = β_max. The critical radius limiting the existence of cusp tori is denoted by the dotted vertical line marked r_mc. The maximum value β = β_max matches the cusp value when r < r_mc and the value implying tori extending to infinity when r > r_mc. For the absolute value of β, only one specific curve is drawn in each panel, $\beta =\sqrt{0.15}$ (marked in grey), which makes it possible to distinguish frequencies that correspond to relatively large tori, as they are displayed below this curve. The dotted vertical lines in each panel marked r_mc denote the radii limiting the existence of cusp tori: any torus with a centre above this radius does not exhibit a cusp. An analogous notation is used later in several other figures.