This paper presents an improvement of a prominent Pixel Value Ordering (PVO)-based Reversible Data Hiding (RDH) scheme. We started with analyzing the rate-distortion performance of the scheme for different neighborhood pixels. Particularly, unlike an image block with horizontal neighborhood pixels considered in that scheme, we proposed a set of blocks of size 3× 2 (or 2× 3) that creates a pair of pixels-trios. In a pixels-trio, two pixels in one row and the third pixel immediately under or above of the other two pixels form a triangular shaped block. This allows a greater possible correlation among the pixels resulting in higher embedding rate with lower possible distortion. We also investigated the case of 3× 1 size blocks with vertical neighborhood pixels. Experimental results demonstrate that the proposed embedding technique with 2× 3 size blocks offers the best rate-distortion performance for USC-SIPI image-set compared to the original scheme and embedding with other block sizes.