I don't often disagree with Rex, but I do this time. Bubbles from either pearling or stick-on CO2 won't remain on the tops of leaves very long. Bubbles float. But, bubbles from any source can easily be trapped under a leaf. So, pearling does generate big coalesced bubbles under leaves. CO2 bubbles, on the other hand shouldn't do that because CO2 dissolves easily and rapidly in water. A big CO2 bubble should shrink quickly, becoming a little bubble.