If you didn't connect solidly enough to damage the ice, then clearly you didn't strike it hard enough to trigger the spell - the spell must have a threshold, after all, since otherwise it would be exploding every time a fly landed on you or a leaf blew onto your shoulder. We determine that threshold by a successful hit that reduces the temp hitpoints.
How about Fire Shield?
Thin and wispy flames wreathe your body for the duration, shedding bright light in a 10-foot radius and dim light for an additional 10 feet.... whenever a creature within 5 feet of you hits you with a melee attack, the shield erupts with flame. The attacker takes 2d8 fire damage from a warm shield, or 2d8 cold damage from a cold shield.
Now that should burn the bugs and leaves, too. It's mostly just a rules mechanical limitation, one a CRPG could easily go around. My stance remains that the damage shields are poorly designed both mechanically and conceptually. I always hated Fire Shield in every iteration of D&D because it assumes you must take damage for it to be at all useful. It's completely counter-intuitive to what a defensive (or offensive for that matter) spell should do in the first place.
