True, but if their using FTL drives that require them to drop back into normal movement at the edge of the solar system we'd know about them long before they got here. The only way they could catch us completely by surprise is if their FTL drives let them go straight into Earth orbit.
Or masking themselves as meteorites/asteroids would get them undetected (or at least wrongly identified) up to the belt beyond Mars.
From there it's a small hop, skip and slaughter to Earth..
Then the other cliché would be to park the mothership behind the moon (we need radar on that side of the moon, STAT!), wait until August and time the actual invasion to coincide with the annual Perseids meteorite shower.