New Aqua Terra 38mm, a little confused about the crown, would appreciate any experience.

I recently purchased the 38mm aqua terra, and when the AD was giving me the instructions and showing me the watch, they explained it had 3 positions: all the way in, 1/2 way out, and fully pulled out.

They said all i need to do is pull the crown to 1/2 position to wind it, then all the way out to set it. They then explained all i had to do was push it back all the way in to return it so its standard and functioning state.

My question: after pushing the crown back in, do i need to turn CW until tight to make sure it is sealed? It takes a very small turn CW (about 1/8 a rotation) to tighten it, but if i just shake the watch, it is loose and is able to be wound again that 1/8 rotation.

Is this normal? I have read through the manual and cannot seem to understand if the crown needs to be wound that 1/8 to be safe for diving use. Is this true?

Thanks for the help.