I tested saber ward (25% absorb) and shield adrenal (30% absorb) together while standing in melt armour puddle of bug WB on ossus.

Each tick of melt armour is always the same: 29978 dmg if unmitigated (with 20% tank iternal DR).

With just saber ward i absorbed 7494 dmg (expected value).

With just adrenal i absorbed 8993 dmg (expected value).

With both saber ward and adrenal, i absorbed 6745 dmg (wth? 25% and 30% absorb results in a 22.5% absorb?).

The above makes absolutely no sense.