Before a drill, players often ask, "Who's doing the drill?" The answer is, of course, both players. And that includes a player who is blocking. But it's more than that - some would say one player is doing a footwork drill while the other is blocking, but that's totally wrong. They are both doing a footwork drill. Good blocking takes good footwork. If you don't move, then your blocking can fall apart like a crumbling wall.
Like all strokes, you block better when you have one basic technique, instead of having to reach to the left or right and alter your blocking stroke to adjust. The problem is that, when faced with a hard-hit ball, that's often what a player reflexively does. But that's the point of practice, so you can develop proper reflexes. Just as with other strokes, the proper reflex is to move to the ball, so you can block each ball with essentially the same stroke, with minimal reaching.
This doesn't mean you never reach for a ball, only that you should train your reflexes so you start by moving to the ball, as well as reaching if necessary. For a righty backhand blocker, this means moving right to cover the middle, and moving left to cover the wide backhand. A key to this is not waiting to see if you have to move - assume you have to move, whether it’s an inch or a foot or more, thereby getting a quicker start once you see the direction to move. This should involve a slight "hop" between shots as you prepare to move - watch videos of top players to see this.
You also have to be able to move in to block. You should normally be positioned so as to block deep attacks, but if a loop lands short on the table, you should move in and block it aggressively.
How do you develop these reflexive habits? Practice! In this case, perhaps have someone loop over and over to one side, backhand or forehand, but intentionally moving the ball around so it sometimes goes wide, sometimes toward the middle. (Below the elite levels, this will likely happen regardless of where they are aiming as they might not have the control to hit these spots - meaning you get good practice moving!) Focus on stepping to each shot and catching them just right, over and over.
Once you do this, you'll find blocking easier and more consistent. And then your blocking will become a wall!