My ebo jaegers are fully submersible. Are you sure the line isn't a mark after which it MUST be submerged? (ie it is fully submersible but if you don;t want to submerse it so you don't get your fingers wet when when adjusting it, you just submerse it to the line and can leave the rest above water?)
This from Aquaticsonline.co.uk:
Jager Aquarium Heaters
Jäger Heater/Thermostats from Eheim Aquatics
A top quality heater/thermostat from Jäger, part of the Eheim Aquatics Group
As a result of the use of DURAN® laboratory safety glass as the glass jacket, heat transmission is excellent, which results in a lower wattage to heat up the same volume of water (300w heats up to 1000 litres)
Model
Watts L mm Ø mm °C Tank Size
200w 200 400 24.5 18-34 300-400 litres
300w 300 500 24.5 18-34 600-1000 litres
Precise adjustable temperature control
Accurate to +/- 0.5°C
Heater on/off indicator lamp
Dry running protection
Fully submersible
1.7m of mains cable
Excellent heat transmission
Special Schott DURAN® shatterproof glass - i.e resistant to cold water shock
HTH
Sarah