Model.json keeps the database length for the column's size. Dataverse has a concept of database length for each column. If you create a column with a size of 200 and later reduce it to 100, Dataverse still allows your existing data to be present in Dataverse. It does that by keeping DBLength to 200 and MaxLength to 100. What you see in Model.json is DBLength and if you use that for downstream processes you will never provision lesser space for your Dataverse columns.