I would start by getting 1 small flat black tube about 1 inch long (could be 1 piece of heat-shrink tubing) and fit the tubing over the photo-transistor. This will make the sensor more directional, but much more capable of sensing long distance.
All the online DIY versions use drinking straws painted black and taped or glued together. Hot glue works with paper straws but melts plastic straws.Tube length is 1/4" to 1/2" . I think any longer than that doesn't work well because it hinders reflection.
If you put a non-inverting
op amp amplifier between the collector and A0 analog input, you can increase the sensitivity.