Panoramic stereo images, captured by distributed devices then mosaicking, are competent contents for virtual reality applications. Mosaicking raw images with different perspectives into satisfying final results is still not efficient enough, even if state-of-the-art algorithms are employed. For improving this efficiency in optical methods, we delve into the potential of the capturing system. Two parallax factors, peak parallax and deviation of parallaxes, are proposed to assess the mosaicking capability. By controlling variables and numerical computation, rules between parallax factors and design parameters have been revealed. Validation by simulations, large capturing distance, more cameras, compact arrangement, and moderate overlaps are suggested as the general design strategy. Benefiting from efficient mosaicking, systems based on our design strategy would have potential for real-time applications.