@samuel-wieczorek Hi Samuel. I positioned the sensor over the 1 liter wheel. I did not used the TCRT5000 module, but made a custom built PCB. Howver the principle is the same (in fact the schematics is 100% the same as the TCRT module.
If you go to https://www.openhardware.io/view/15/Itron-Aquadis-watermeter-sensor-V10 you can see pictures of the module. Some tips I can share with you:
Shield the sensor and the rotating disk area from incoming light. This influences the sensor. Use a piece of plastic tube for example. In NL we have electrical wire tubes that can be used (the grey ones)
Bring the sensor close to the disk. The reflection should do the rest. Setting up the TCRT is tricky as you have little room to manouver (considering reflection and the point where the schmit trigger swaps state)
Be aware that when the disk stops with the edge near the sensor you get false readings. That is why I swapped to a software driven solution using SW hysteresis on the arduino.
Hope this helps. If you can open it, I can share a DXF file with the sizes of the bottom plate I use. Let me know!