Nix /home to docker installation problem

imagex.nix

mypkg = mkDerivation rec {
  name = "mypkg";
  version = "0.0.1";
  src = ./.;
  # ...
  outputs = [ "out" "custom" ];
  installPhase = ''
    mkdir -p $out
    do-some-install-to $out
    mkdir -pv $custom/share
    cp -dR --preserve=mode,timestamps from-sources-share \
      $custom/share/custom/
    mkdir -p "$custom/home/custom"
    ln -Tsv $custom/share "$custom/home/custom/share"
  '';
}

let
image = with dockerTools.buildLayeredImage {
  name = mypkg.name;
  tag = mypkg.version;
  contents = [ mypkg.all ];
  created = "now";
  config = {
    Entrypoint = [ "myapp" ];
    ExposedPorts = {
      "4000/tcp" = {};
    };
  };
}
in image

Currently $custom have such output:

├── home
│   └── custom
│       └── ...
│           └── share -> /nix/store/fmkqf6zyql85wrirdxasdh9i804a9g98-mypkg-custom/share
└── share
    └── ...

But I see only /share linked to dockers root at result docker image.