Z Thickness of Part

[mcdavidr 0]

I am struggling with my Anycubic I3 Mega. Parts I print turn out too thick. If the parts is designed at 4mm thick, it prints at 4.2mm or so. How does Cura determine finish height? I set the nozzle to bed gap at .15mm, Initial layer height .25 to .3mm. Does Cura calculate this?  Some flat parts I can just scale down the z dimension. More complex parts I position the bottom below bed level. Is there a setting I am missing?