Heritability refers to trait variation due to genetic variation within a population. This is different than the amount genetics actually contributes to a trait

Heritability refers to trait variation due to genetic variation within a population. This is different than the amount genetics actually contributes to a trait. While you are controlling for environmental factors in heritability studies you are still referring to a specific population. It can be the case that two identical genotypes across two different populations show two different phenotypes.