Hi Efrye,
To debug and adjust LPV you would want to use the option in the viewport for Show > Visualize > Light Propagation Volume.
It will look something like this with default settings:
The “blockiness” that you refer to is normal. LPV uses block volumes to calculate and inject light into the scene.
4.8 may have some newer code from Lionhead Studios, but I’m not sure where this stands at the moment with the rendering team and if it’s been integrated yet.
Also, the scene you linked to, is not necessarily a good example since it’s using foliage vs block geometry where some of the tweaks would be more noticeable. At the moment I’d say keep on using where possible and have fun with it. Once the new code is integrated there may be a significant improvement or at least more options to tweak for better results. This should hinder from developing other parts of your project in the meantime. 
I hope this helps.
Tim