Shield and I-frame Interactions.

By: Trosalio#0420 Added: 2021-06-03 Discussion
Finding: Gaining I-frames by dashing through enemy attacks will allow both your unit and their shield to take no damage, but using an Elemental Burst to gain I-frames will only make your unit took no damage, while their shield will still take damage.
Significance: better knowledge of how to preserve shields and how shields interact with I-frames.

Damage Reduction Applies Before Shields Are Calculated

By: Faranight#0001
Damage reduction applies before shields are calculated.
Shields are more effective on characters with high defense.

How Elemental Shields having 250% Absorption Bonus to said element Work

By: Türin#8565
E/N: Submission demonstrates the above mentioned effect using the example of Diona but this also holds true for other similar character-generated shields.
With Cryo Absorption Bonus, Diona takes 2.5 points of Cryo Damage for every 1 point of Shield HP lost.
My original math is in the description of the video.
Other shield effectiveness is not accounted for, but it stands to reason that they work the same way. We can both say that a shield has 2.5x of its current value, or the damage is reduced by 2.5x, against it's effective element.