Conventional approach, unless specifically instructed otherwise, the spring mass is greater at the tighter wound end (softer part of progressive spring) that beneficial to be placed at the most static point in assembly next to head casting.
My understanding is that it makes no difference to spring rate operation, it'll compress the softest part first whichever direction fitted. But, the harmonic characteristics are fundamentally shifted when mounted with increased mass located at the most moved part, that at valve cap/collar which offers most benefit in valve train attribute for being as lightweight as possible.
