[DnD 5e] Disciple of Life + Upcasting

your healing spells are more effective. Whenever you use a spell of 1st level or higher to restore hit points to a creature, the creature regains additional hit points equal to 2 + the spell's level.

What happens when I cast a level 1 spell using a level 2 spell slot?

Literal reading would suggest that the spell slot is irrelevant only the inherent level of the spell but I have seen statements to the contrary.

It's not a huge difference. But I'd still like to know.