Hi Chris,
Do you mean that the name of the form is "website download" and Each time a submission is made to this form, all Leads whose Lead Source is this form are scored, regardless of the contact person who made the submission?
It cannot be achieved for the Lead Scoring Models are targeting at the Contact or Account.

It means that models are based on the behaviors of Contacts or Accounts.
For example, here are the submissions of a form.

The contact F2 has one submission and F4 has two.
If I set each submission will get 5 points,

the leads whose Existing Contact is F2 will get 5 points, while the leads whose Existing Contact is F4 will get 10 points.




You can find that “Only leads associated with parent contacts or accounts can be scored” in the following documentation.
Create lead scoring models (Dynamics 365 Marketing) | Microsoft Docs
So Lead Source cannot be used as a basis for differentiating Leads in a Lead Scoring Model.
The number of Form submissions cannot be counted in isolation from Contact either.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya