Amortized Cost by Usage: Amortized cost distributed across subscriptions, machine series, enrollments, regions etc. For VMs that benefited by reservations, CloudHealth will calculate the amortized cost of reservation and map amortized cost to respective subscription, region, series of that VM. If there are any unused RIs then their amortized cost will be shown under "Other" because no VM got benefited by a reservation and as such there are no associated subscriptions, series etc.
Amortized Cost by Purchase: When a reservation is purchased, we can buy either single scope or shared scope. If it's single then that reservation has associated subscription but if its shared then no associated subscription. If a reservation is single scope, then we calculate amortized cost of reservation and map it to subscription under which it was bought, region in which it was bought, series of reservation etc. If a reservation is bought under shared scope then it's amortized cost will go under Shared category.