Here's the relevant line of code that replicates how HOME ingests the ZA entity and updates its contents:
https://github.com/kwsch/PKHeX/blob/06c742ac789f31831ab01ed0ec3b62f9fd2847fd/PKHeX.Core/PKM/HOME/GameDataPA9.cs#L129
Size ratings in S/V use the Scale value. In games with separate sizing for height and weigh (like LGPE/E) they use height and weight values. Transferring around in HOME, HOME tries to make things consistent in its own way.