The point of modafinil is remove the need for sleep. You might say it interferes with sleepiness. It may be surprising, but it turns out that sleepiness is not necessary for sleep. Indeed, going to bed early when changing time zones is a demonstration of this, but many people find it a challenge.

People on modafinil are not sleepy at their normal bedtime, but many of them report not having difficulty getting to sleep if they choose. I think more people on modafinil have problems failing to sleep because they forgot or got distracted than fail after getting in bed.

In contrast, most people report that caffeine or amphetamine before bed causes their minds to race and interferes with sleep, making it difficult and low quality.