[question] Problems combining Conan packages with CMake External Project #7636

include(${CMAKE_BINARY_DIR}/Conan/conan.cmake)
conan_cmake_run(REQUIRES dcmtk/3.6.5
				BASIC_SETUP
				CMAKE_TARGETS
				GENERATORS cmake_find_package cmake_paths
				OPTIONS ${CONAN_OPTIONS}
				BUILD missing
This installs the required package (with transitive dependency openjpeg) and creates some output files, like conan_paths.cmake, conanbuildinfo.cmake, FindDCMTK.cmake and some more. The result is, that I can use
find_package(DCMTK)
if(TARGET DCMTK::DCMTK)
endif()
where the condition is true.
This is done before the superbuild starts. After installing Conan packages I include my SuperBuild.cmake, which again includes something like CMakeExternals/DCMQI.cmake. This file does nothing more than calling
ExternalProject_Add(DCMQI
with DEPENDS DCMTK::DCMTK.
What happens now is that I get the following error message:
Make Error at CMakeLists.txt:271 (find_package):
Could not find a package configuration file provided by "DCMTK" with any of the following names:
    DCMTKConfig.cmake
    dcmtk-config.cmake
  Add the installation prefix of "DCMTK" to CMAKE_PREFIX_PATH or set
  "DCMTK_DIR" to a directory containing one of the above files.  If "DCMTK"
  provides a separate development package or SDK, be sure it has been
  installed.
-- Configuring incomplete, errors occurred!
The relevant file / line is here.
So I was hoping that DCMQI uses the FindDCMTK.cmake that was automatically created by Conan but I don't know how to point DCMQI to this file. In our current setup we have a customized FindDCMTK.cmake but CMake also provides a FindDCMTK.cmake.

Here a DCMTK_DIR is defined.
I found DCMTKConfig.cmake inside .conan/data/dcmtk/3.6.5/_/_/build/a77c0a86db5a3776d765c3fb20cfeda3833b0e78\build_subfolder and hard-coding this path also makes the error go away.

But using fixed paths is not an option. I was trying to find a variable created by Conan (inside FindDCMTK.cmake) that would allow me to point DCMQI to DCMTKConfig.cmake but all I see is variables pointing to .conan/data/dcmtk/3.6.5/_/_/package/a77c0a86db5a3776d765c3fb20cfeda3833b0e78/ (package instead of build).
I'm missing some insights here and would like to understand how to resolve this error and what the different package directories are used for (build and package).

Also I would like to know why DCMTK_DIR needs to be set and why the Conan-created FindDCMTK.cmake does not set the variable.
To make things more clear I will probably push the code I have so far this week and post a link to the repository here.
 I've read the CONTRIBUTING guide.