Scaling down player for bigger world space- precision / physics issues?

I know the default playable area for physics and precision to work properly is 5km, my question is, if I want to get 10km by scaling the player down to be half the size, or 20km to be 4 times as small, will this affect physics and precision? How much would scaling down effect this? And if not much, how far down can I go? I’m making a 3rd person shooter with vehicles, so the vehicles would be scaled down as well. I dont see how half the size could be that bad, is it?

Half the size may be fine but you shouldnt go smaller than that. You’ll also have issues with lighting together with physics.

If it’s intended to be single player, it’d be far easier to use World Origin Shifting than to change the scale of everything.

There’s a note on that page that gives some multiplayer guidelines, as it’s not going to work well out of the box. Depending on your needs it could be simple or difficult to accommodate shifting in a multiplayer scenario.

Thanks for the answers
And yes my reason for doing this is because multiplayer isnt really supported with world compositor & origin shifting since my game is not coop, players are spread out, I’m hoping TechLords MMO Plug-in will solve this, since having only 5km of playable space per map on a different server is not a very good workaround for games with vehicles, so much loading and reconnecting!
https://forums.unrealengine.com/showthread.php?22928-Next-Gen-MMO-Plug-in-for-UE4&highlight=mmo