API:v2/commerce/exchange/gems with different quantities

Hi,

how does this endpoint calculate the "coins_per_gem" when using different quantity values?

Examples:

https://api.guildwars2.com/v2/commerce/exchange/gems?quantity=10{"coins_per_gem": 1870,"quantity": 18706}

https://api.guildwars2.com/v2/commerce/exchange/gems?quantity=100{"coins_per_gem": 1978,"quantity": 197839}

https://api.guildwars2.com/v2/commerce/exchange/gems?quantity=1000{"coins_per_gem": 1981,"quantity": 1981494}

https://api.guildwars2.com/v2/commerce/exchange/gems?quantity=10000

{  "coins_per_gem": 1968,  "quantity": 19680532}

All requests are made at the exact same time.

I understand, that with larger quantities there could be some rounding-differences. But this differences do not look like this.

Is there an explanation for this differences in the "coins_per_gem" value?

Thanks.