I dont use Ultra pac anymore.
For draft marks and situations like Davids, I use strong dose of enzall and citrus contrate together (could also try power burst and citrus concentrate together). Then rinse with the usual formula 90 in the tank (i always use f90 as a rinse) The results are always 100%.
Did a rich client a couple of years a go (lives in a very modest house but owns over 30 properties and goes off skiing in France 6 months of the year) and I removed some draft marks that a previous carpet cleaner refused to do as they told him that trying to remove the draught marks only makes them worse!
Needles to say that customer now gives me alot of work!

Tony