We employ combined smoothed particle hydrodynamics (SPH) and molecular dynamics (MD) simulations to systematically investigate the evolution of micro‑jetting from tin targets with sinusoidal surface perturbations under twice‑shock loading. Results show that the initial scaled amplitude k0h0 critically controls the bubble morphology after the first shock and the subsequent coupling behavior of second-shock ejecta: a smooth single bubble forms at k0h0 = 0.25; for 0.50 ≤ k0h0 ≤ 1.20, a single micro‑spike splits the bubble into two sub‑bubbles, leading to two second jets that first diverge and later merge under strong mode coupling; for 1.40 ≤ k0h0 ≤ 2.00, two micro‑spikes divide the interface into three sub‑bubbles, producing three independently growing micro-jetting with markedly weaker coupling. To predict the second-shock ejecta mass across this wide k0h0 range, a new approach is introduced that treats the post‑shock bubble interface as a multi‑mode perturbation. Through Fourier modal decomposition and incorporation of inter‑mode coupling, a predictive model is developed that shows good agreement with simulation results. The effectiveness of the computational approach is further validated against existing second-shock micro-jetting experiments. This work elucidates the physical linkage between initial surface conditions, shock‑induced interface morphology, and jet‑coupling dynamics, providing a quantitative framework for the prediction of ejection under multiple‑shock loading.