In Formulary IG 2.0, the Payer Insurance Plan Profile (InsurancePlan Resource), which represent plan coverage level information, has Drug Tier ID (path- InsurancePlan.plan:drugplan: benefit.type), the Binding of the field is shown as required. Please refer screenshot 

Where as in the Formulary Item Profile (Basic Resource), which represents Formulary  Drug level information, has Drug Tier Binding as extensible. Refer the screenshot.

Question 1: Is there a reason why 2 different binding strengths are provided for Drug Tier on Plan Level v/s Drug Level ?

Point: 

In Formulary IG 1.0, the Drug Tier ID binding was extensible. Thus we added custom options to match what is being currently offered by the organization.

For example: 

Tier 1 - "Generic and Brand"

Which means a single tier for a plan offers both Generic and Brand Formulary Drugs.

Question 2: Thus, is there a way we can provide custom drug tier options on the Plan Level in Formulary IG 2.0 under Payer Insurance Plan ?