The infinite uniformly charged plane and the parallel-plate capacitor are two fundamental idealized models in the electrostatics section of electromagnetism. However, students often confuse the electric-field formulas near these two models, $E=\sigma /(2{\epsilon }_0)$ and $E=\sigma /{\epsilon }_0$, which leads to cognitive conflict. This paper analyzes the origins of this difficulty and shows that it mainly arises from confusion between the field-superposition mechanisms of isolated and coupled systems, a rigid or inappropriate application of Gauss's law, and insufficient construction of physical pictures of field distributions. On this basis, a four-step instructional reconstruction framework is proposed, following the sequence of “model tracing, principle analysis, physical-picture construction, and methodological comparison.” By emphasizing the central role of the superposition principle and comparing the physical meanings of different Gaussian surface choices, this framework guides students to construct a clear physical picture of electric-field distributions. It thereby helps resolve the cognitive conflict at a deeper level and improves students' conceptual understanding of electrostatics as well as their ability to transfer and apply core ideas. physical picture of electric-field distributions. It thereby helps resolve the cognitive conflict at a deeper level and improves students' conceptual understanding of electrostatics as well as their ability to transfer and apply core ideas.