While standing inside well of radiance you are not counted as "radiant" so the grenade damage buff from the artifact perk "sheildcrush" doesn't apply its grenade damage boost while radiant until you step outside the well of radiance. Once you become radiant from either stepping outside the well or applying radiant through your melee you can then step back into the well and keep the damage buff for the duration that you would be counted as radiant from either of those 2 methods. This same effect happens with the artifact perk "Torch" that is a part of the queensfoul censer artifact. Due to well of radiance not counting you as radiant you will not get the increased weapon damage on targets affected by stasis or strand until you again, gain radiant by stepping outside the well then back in or by any other means.