Archera's GRI allowances & premiums are set primarily set based on market liquidity as assessed by Archera's dynamic underwriting algorithm. This means for certain instance types, services & regions the number of GRIs available to purchase from Archera can be much lower than for others. This is based dynamically on the amount of demand for the commitments in the marketplaces Archera has access to.
For example Archera tends to offer the highest GRI allowances for common EC2 Instance types in the most popular regions, given these are the most popular & in-demand commitment types. However for less popular RDS instance types, which are not as in-demand as EC2 instances, the allowance can be much lower & average premiums higher.
There are also specific ways individual customers can increase their overall GRI allowances as outlined here.