I install the facet and turn on the water a little over half way and the shower come on with the shower button pushed down. If turn the water less then half way the shower will not come on??

I install the facet and turn on the water a little over half way and the shower come on with the shower button pushed down. If turn the water less then half way the shower will not come on?? By turning down the water less then half way you reduced the pressure needed to force the water up the shower raiser. This is normal, Good luck, Tom