It's 40% of the _starter dose_ (2.5 mg), which is what patients begin taking to get their bodies accustomed to the drug. The "maintenance dose" that patients build up to can be many times higher (10-15 mg).
40% of the starter dose (40% of 2.5mg = 1mg) would be between 6-10% of the "maintenance dose" (betweeen 10-15mg).
40% of the starter dose (40% of 2.5mg = 1mg) would be between 6-10% of the "maintenance dose" (betweeen 10-15mg).