An approximate equilibrium-satisfying solution for the Reissner–Mindlin (RM) plate can be obtained by expressing the plate section forces using the Southwell stress vector function. In [1], the RM bending problem was solved using a C1 triangular Hsieh–Clough–Tocher (HCT) element, for which stress boundary conditions are imposed as linear constraints on nodal degrees of freedom. While effective for hard (two-dimensional) boundary conditions, this approach leads to an excessive number of constraints when applied to soft (three-dimensional) boundary conditions. To avoid overconstraining the nodal unknowns, the present formulation introduces an additional Airy stress function for bending and twisting moments. Consequently, the employed HCT element possesses 36 degrees of freedom. As an example, the solution for a rectangular steel plate of dimensions 1.5m x 1m and thickness 0.2m, subjected to a uniformly distributed load (p = 1kN), is found. The load is equilibrated by forces applied along short segments near the plate corners. The results are compared with a kinematically admissible solution obtained using a 22-degree-of-freedom element with cubic and parabolic interpolation for deflections and rotations, respectively, [1]. The error estimated by the Synge method [2] does not exceed 0.8% for a fine mesh, indicating close agreement between the dual solutions. [1] Więckowski Z., Świątkiewicz P., Equilibrium-Based Finite Element Analysis of the Reissner–Mindlin Plate Bending Problem, Materials, Vol. 18, 4969, 2025. [2] Synge J.L., The Hypercircle in Mathematical Physics, Cambridge, Cambridge University Press, 1957.