Thanks for your reply and I have contacted the author.
There is another question I encountered in heritability analysis. I have done a heritability estimation of height adjusting for sex, age, age square, and their interaction. The result was that the heritability estimation of height was 0.612 and the covariates explained 0.518 of the trait variance.
Theoretically, the sum of heritability and covariates' effect should be less or equal than 1. But here, 0.612+0.518=1.13>1.
The code is as below:

trait height
cov age^1,2#sex
polygenic

Do you have any idea about this?