The MVC+D extension of the Advanced Video Coding (H.264/AVC) standard enables multiview-and-depth 3D video coding but specifies that all views are coded at equal spatial resolution. In mixed resolution 3D video coding some of the views are coded at reduced resolution. This paper proposes an improvement for the mode decisions in depth encoding in the mixed resolution scenario. We modify the distortion calculation for rate-distortion optimized depth coding. The proposed solution optimizes the depth data compression with assumption that it will be used not only for view synthesis but also for depth-based super resolution in the post-processing stage. The algorithm is implemented on top of the mixed resolution 3D video encoder based on the 3DV-ATM reference software. Evaluation of the proposed solution, tested under the JCT-3V common test conditions, is done against the mixed resolution MVC+D coding with the view synthesis distortion enabled. The results show 2.64%dBR gain for coded views and 0.64% gain for synthesized views.