A planar problem of diffraction of an acoustic cylindrical wave at a convex shell of arbitrary form is considered. The interaction of the shell with the acoustic field in the medium is modeled by a boundary condition containing the second derivative along the tangent to the shell, in addition to the function and its normal derivative. The wave field scattered in the sonified region is represented by uniform asymptotic expansions in inverse powers of frequency, which provide insight into the formation of a head wave that is induced near a critical ray in the medium by oscillations propagating in the shell. Far from the critical ray, these formulas describe the reflected wave and the head wave propagating on their own. A physical analysis of the main terms of these asymptotic expansions is presented.