Oscillation amplitudes of the spin Ω₂ (top row), the lag angle δ₂ (second row), the equatorial flattening (third row), and polar flattening (bottom row) of a Kepler-38-type planet around the pseudo-synchronous solution. The different colors indicate different methods of obtaining the amplitudes: numerical in black, analytical up to zeroth-order in green, up to third order in red, and our new simplified model in blue. The dashed black lines represent the numerical mean solution. The different columns represent different planetary eccentricities: e₂ = 0.05 (left column) and e₂ = 0.1 (right column).