From: Rabbi Moshe Sofer
To: Rabbi Moshe Perles
The Chasam Sofer rules that a brother cannot invoke a kim li claim to benefit a third party — specifically, to divert assets from the married sister (holder of a shtar chatzi zakhar) to the unmarried sister. He further argues that when a first daughter was already married off during the father's lifetime, both Geonim agree the second daughter receives an equivalent dowry even if it exceeds a tenth of the estate, making this close to the letter of the law rather than merely lifnim mishuras hadin. He also rules that the custom of giving a shtar chatzi zakhar does not apply to an orphan daughter marrying after her father's death.
Source: Shu"t Chasam Sofer CM §183