All the spacing in the templates is generated automatically by the system. It might differ based on the number of products, length of notes and terms, and other information such as QR Code, HSN Summary added.
Unfortunately, we do not have much control over this aspect as it is system generated.
In order to edit the document manually you can go to Document Settings and try setting the top and bottom margin as desired.
You can also try out different invoice templates.
If the number of products are more, we suggest you to please use Compact invoice template and check.