build fails with 0.18.5 (worked in 0.17.4)

First, a related question that could help me: Where is the documentation for ncc?
The readme file leaves many open question (at least for me as a beginner). And due to this lack of documentation I don't even know how ncc is supposed to work or which questions to ask. So I'm afraid, I must explain the whole use-case.

The build on our CI server was still okay with version 0.17.4 - but now fails with 0.18.5.
To me it seems, that ncc is now somehow finding our top-level tsconfig.json file and it tries to build the whole source code - which will not work, because we have a mono-repo and thus have many different tsconfig.json files.

This is how our code is organized:

• tsconfig.json - top level ts config
• angular.json
• .. other files
• apps dir
  • client
    • tsconfig.app.json
    • tsconfig.json
    • tsconfig.spec.json
  • server
    • tsconfig.json
  • ...
• libs dir
  • shared
  • ...
• node_modules dir
• dist dir
  • apps
    • server
      • main.js - created by the prod build
      • tsconfig-json - created by our ci-script for ncc - content from your readme file

The ci script will first do a regular ng build of the server app which creates dist/apps/server/main.js. Then the ci script will cd to apps/server/ and execute ncc build main.js --minify --out ncc to build ncc/index.js.
It seems that the newer ncc version will traverse the folder tree up, find the top-level tsconfig.json file and then tries to compile all source code: e.g. in apps/client/... - which will fail, because the top-level tsconfig.json file is not suitable for that source code.

As a workaround I tried to delete the top-level tsconfig.json file - then the build works.

Questions:

1. Why would ncc even try to start the typescript compiler? it already gets the main.js file?
2. Why would it use the top-level tsconfig.json, when there is a tsconfig.json file in the current directory?
3. Can I somehow configure which tsconfig.json file it should use?