This could be due to the sensor being shielded by the window sash on a steeper pitch.
Velux skylight rain sensor problems.
The rain sensors work when they get wet.
A velux skylight installed with a velux flashing kit is guaranteed leak free for 10 years.
If there is an issue with the effectiveness of the rain sensors it will be subject to a service request from velux.
A wire extension can be ordered directly from velux to accommodate moving the sensor panel.
Based on the above we should expect to get paid for the installation that delivers what it promises.
The rain rain sensor on the solar powered fresh air skylight seen here is the small gray box on the right side of the panel attached to the bottom of the skylight.
Velux has a remedial option if a customer insists the skylight closes whenever it rains.
In this case the rain sensor may need to be relocated.