Confused with Wattage to use on Legend 5

Hi All - Total noob here. Following all the great advice, I have a Aegis Legend 5, Fat Rabbit Tank and 0.5 ohm GT coils. My first try at this. This vape has 'SMART' mode that recognizes the coils as 0.44 (dunno why it doesn't see 0.5), and sets that wattage as 54. Apparently it 'recognizes' the correct wattage to use. But advice on here says 20W is the sweet spot. What do I do, try and dial in down manually (that seems to be available as 'CUSTOM')? I guess, I just want to not break anything.