A method for video decoding includes decoding prediction information of a current block, the prediction information indicating a sub-block based inter prediction mode, the current block including a plurality of sub-blocks arranged into one or more areas. For each area, the method includes determining base motion vectors of a portion of the sub-blocks within the area, the portion including at least one non-corner sub-block of the current block, and converting the base motion vectors of the portion of the sub-blocks into respective target motion vectors. The method further includes generating reconstructed samples of the corresponding area according to the target motion vectors of the portion of the sub-blocks, and reconstructing the current block for output based on reconstructed samples of the one or more areas