When I throw a splash or lingering potion on a block, I expected for it to splash it's corresponding effects on where the potion landed, not splash adjacent to where the potion landed. Below is a video link showing what
I mean. Before watching the video, I highly suggest you to watch in the speed setting 0.5 or if necessary 0.25 so you closely see the potion's splashed effects splashes adjacently to where the potion lands on a block.

Video link: https://www.youtube.com/watch?v=BdnGCFBu0Q8&feature=youtu.be