i completely agree.
im at around 17-22s with fridrich.
yes, i know that kind of range is ridiculous at around 20s... but its true!
if ive had a rubbish day, for example, cubing rarely cheers me up. in fact, i generally just get angry and throw it around... and i average sup 20.
whereas on a good day, when im not too hot or cold, and ive been warming up for a while, i can bust out very consistent 15-19s times.
i think technique also has an underrated influence on cubing - even if i lookahead well, if my turning isnt accurate then ill just pop and lock, and that distracts me, and ill get like a 24. but then if ive been doing it for a while, and feeling confident my technique just goes through the roof, and with roughly the same lookahead i can happily bust out a sub 15... its very peculiar.