For HF, look at the technical articles by PA3WFM for the WebSDR at utwente.nl, especially this one: https://www.pa3fwm.nl/technotes/tn07.html

TL,DR: you probably don't want a random wire for HF reception, but either an E-field whip antenna like that one, or an H-field loop which will likely be larger and more expensive, but will have useful directional properties that the whip will not.