So the problem is that I'm unable to get some detail from highpoly to lowpoly, some pictures to demonstrate.
Low and highpoly together.
Shell with highpoly under it.
Result is that there is no depth, or very little on the outer cavity wall, i tried adjusting shell size and adding/removing edge loops but nothing really helped. Originally i had a small cavity in the lowpoly model to match the highpoly, but it produced pretty bad quality maps.
And this is what the highpoly looks like.
Also got a second question, is there any way to get rid of this uneven edge shown below