Compatibility levels are unified; regardless of how many items you sync, the required compatibility materials increase incrementally.
For instance, if you only sync one item, moving from level 1 to level 2 requires one hundred compatibility points, then level 2 to level 3 requires three hundred, and level 3 to level 4 requires one thousand.
Now, if you sync two items, the levels are calculated separately, but the required materials are not calculated separately. Take Li Yao, for example, he synced the Mother Worm and Heart of Machinery.
Li Yao has raised the compatibility level with the Mother Worm to level 2, so if he wants to raise the Heart of Machinery to level 2, it will require three hundred compatibility material points, and so on.
Later, raising compatibility levels becomes increasingly difficult, especially after the ninth upgrade, where it becomes even harder.
Therefore, people often sync with just one item.
