Yeah, small pieces can slip through the grate if you're not careful. Arrange them perpendicular to the grate to lessen the chance of that happening.
Also, next time, try placing the foil on the non coal side of the coal grate instead. This will aid in the convection effect in the kettle dramatically.
....UDS....Mini-WSM....Midi-WSM....Mod-ECB....22.5-OTG....34"wood fired pizza oven....