There will be no I’ll effects other than more turbulence directly out of the bottoms of your standpipes due to increased pressure from the smaller diameter as well as some loss of total flow. Not a huge deal though.
Is your loc- line at least the same diameter?
I have no loc-line in the overflow drain setup.
If your asking about my return it is plumbed 1” up to the top of the tank then is connected to 3/4” loc line.

