it does not work if the sensor is underneath

i could build a device which you can put on the table and looks to the candles
it has 80cm of recognizing a flame.

it would use the following components
Adafruit ESP32 Feather V2 
ANGEEK KY-026 Flame Sensor Module
2000 - 3000 mah LiPo

battery life would be 20 Days, cost would be around 35€ just plain devices cost without work time
3d printed housing would be needed