In that case, it's better practice to use configurable product url as entry point, for example nike-shoes. On all simple products (lets say thay you have size & color variations), just append their parameters naturally, like nike-shoes-blue-40, nike-shoes-blue-42, nike-shoes-green-42...
There is no reason to use the same URL keys when Magento will append number at the end, which looks awful.
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