Hachirin-no-obi and opposite Element Day penalties

Hi SE,
Myself and a few friends were discussing today how the combined Hachirin-no-obi appears to retain both the elemental bonus and penalty for corresponding elements of a particular Elemental magic spell. (So, a Thunder spell cast on earth day could be subject to a -10% penalty and simultaneously, with Thunder Weatherx2, gain a +25% bonus).

Meanwhile, Cure spells, which seem to be the exception, benefit from Light elemental weather bonuses but unaffected by Lightsday or Darksday.

Is this just simply a feature of the single, individual elemental belts themselves (Anrin Obi, etc)? I must add that, it is also certainly a feature of the Hachirin-no-obi as well...or ...is the Elemental-day Penalty just a permanent fixture in Vanadiel regardless of the belt?

Thanks SE!