A Safety Quantity can be used to subtract a number from the available quantity. For example, if there are 5 units available and the Safety Quantity is 1, only 4 will be sent to Amazon.
This can be set on a company level so it defaults for all products, but it can still be overridden on a product level on the Amazon Properties page.
Each channel has a default company-level safety quantity and a product-level safety quantity. On the channel's Settings page, there are two safety quantity settings - one for regular products and one for replenishable products. Typically, Safety Quantity can be set to 0 for replenishable products because there is no strict inventory for replenishable products.
Another option is to set percentages of available qty that should be sent to each channel.