The answer to this question is provided by the European Commission.

Article 84 of Commission Delegated Regulation (EU) 2015/35 sets out cases where an insurance or reinsurance undertaking is required to apply the look-through approach.
Article 171 of that Delegated Regulation sets out the criteria to be fulfilled by a related undertaking to meet the definition of equity investment of a strategic nature.
Where the look-through approach has to be applied to a related undertaking pursuant to Article 84, such a requirement cannot be waived, even if that related undertaking fulfils the conditions of Article 171 of Commission Delegated Regulation (EU) 2015/35.

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The answers clarify provisions already contained in the applicable legislation. They do not extend in any way the rights and obligations deriving from such legislation nor do they introduce any additional requirements for the concerned operators and competent authorities. The answers are merely intended to assist natural or legal persons, including competent authorities and Union institutions and bodies in clarifying the application or implementation of the relevant legal provisions. Only the Court of Justice of the European Union is competent to authoritatively interpret Union law. The views expressed in the internal Commission Decision cannot prejudge the position that the European Commission might take before the Union and national courts.