I will use an Emerald Crater for example. This is a standard map:
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And if middle will get some more mexes it will become more valible to play for it instead of side expansions. Examples(different colors - different variants):
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Or if some mexes from clusters will get spread, so it'll become easier to raid, harder to take and defend:
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Or if some civilians will appear in these zones:
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My suggestions about this particular map might be bad, but i hope you understood my general idea.