You need to rethink your feeding. A healthy well fed brb at that age should be talking food much bigger than a rat fluff. They have very little calcium in them.
I would suggest feeding twice weekly, perhaps with a rat fluff for one meal and a small mouse the other. That way your snake will get the calcium it needs to develop healthy bones.
At a year and four months its still growing so I fail to understand why you would want to reduce the food I stead of increasing it.
Having looked at the image, that snake is seriously stunted cornice age. A nearly 18 month old brb should not look like that when it's taken a rat fluff.