Your blur horizon is primarily affected by the amount of correction you wear relative to the object you are trying to see.
How blur horizon is applied
For differentials, the blur horizon is just enough to see the object.
In most cases, this is a screen. By wearing differentials, you increase your blur horizon just to the point where you can see the screen clearly, but the rest of the world is still somewhat or very blurry without wearing stronger correction. This is perfectly fine and part of the plan - differentials are only meant to correct you for a set distance.
For normalized, the blur horizon is nearly unlimited.
Emphasis on nearly - it is crucial for the blur horizon to be slightly undercorrected and challenging your vision when compared to a full correction an optometrist is likely to give you. Being slightly undercorrected is perfect, as too much undercorrection will both stagnate improvements and cause you to live in blur unnecessarily.