I think its easier to pick them if you convert it to Tile coordinates. That way you can just add integers values as distance to what you want to pick. Here is a very simple example:
Now in this case I have just chosen a fixed point of the table at (2,2) but it would be the same if it weren't fixed, and then I use a Range variable to set the desired range.
So you just have to convert the mouse click to a tile coordinate or the sprite thing you use, which you can do with PositionToTileX and PositionToTileY.