Resonance bonuses regularly visible on the Attributes page are not added to the Trial Character's Attributes page. Pyro Resonance not being applied is also effective in damage calculation. Having the Trial Character be the 5th or 4th party member does not make a difference.
All Trial Characters in Story Quests and Hangouts (including untested characters) are expected neither to be affected by Elemental Resonances, nor to contribute to any Elemental Resonances (including untested Resonance bonuses). When testing and verifying damage calculations with Trial Characters, this interaction with Elemental Resonances should be considered.
Swirl Chain Reactions Can Trigger Electro Resonance