X-ray luminosity of an ultracompact transient system with a He disc, for different values of the viscosity parameters α_c and α_h. Top panel: α_c = 0.02 and α_h = 0.2; the blue curve shows the case where the inner disc is truncated at a variable radius with time, according to Eq. (7), and the red curve is for a fixed inner radius (2 × 10⁸ cm). The mass-transfer rate is 3 × 10¹⁵ g s^-1. Intermediate panel: changing α_c. Same as above for a truncated disc, with α_c = 0.04 (red curve) and α_c = 0.01 (blue curve); α_h = 0.2 is unchanged. In the case of the blue curve, the mass-transfer rate has been reduced by a factor 3. Bottom panel: changing α_h. Same as top panel, with α_h = 0.1. α_c = 0.02 is unchanged.