So, each country's supply centers are squared, then all added up. Each players score is their centers squared/ the total. The total will be a percentage, so a solo is worth 100

, which is catchable.
With this scoring system, you will score a ton if you're at 12 and everyone else is at 3. You'll score a lot less with a 17 17 draw. That's an extreme example, but you can score better at 12 centers and a very balanced rest of the board than with a two or three way.
I feel like it encourages playing the whole board so you can keep players in the game and keep the board as balanced as possible. It's still always in your interest to take centers if you can hold onto them, but it's better for you to keep a small player in the game rather than let them be gobbled up by a rival.