Okay...it would appear this is an easy issue to remedy. Simply use a double charcoal grate setup, two grates at 90 degree angles. Or purchase a piece of stainless steel screen and cut it to fit your charcoal basket or make it the size of the charcoal grate. That will prevent any and all small pieces from falling through. Get it on Amazon.
With lump coal, it's the nature of the beast to have irregular sizes with smaller pieces. Makes no difference what brand you use.
See photo here of dual stainless grates:
And here, standard Weber grates: