I have regenerated the tables in such a way as to build broader "dc" tables. The new generator code is as follows, and the optimal table was generated with a quality of 99.
#ifndef generate_universal_tables
long total = 0;
int has_over_15 = 0;
for( i = 0; i < 256; i++ )
{
if( freq[i] > 0 )
printf( "freq[%d] = %d\n", i, freq[i] );
total +=...
