what is the trend of density down the group in alkali metals. please explain with all exceptions

the density increases down the group in s block elements excpt tht of Na and K it is due to d abnormal increase in size of K.

{size} directly proportional to {volume} inversely propotional to {density}

In alkali metals, atomic volume increases when we go down the group.

You can also conclude this from Lother Meyer's Curve where the atomic volume of Cs>K>Na>Li