Therefore, it is my feeling that when people say a fainter line means you are closer to the "threshold" this is actually inaccurate.
Inaccurate because those people are merely speculating, since drug assay kits lack the ability to give a quantitive value (unlike the GC/MS test).
I was able to produce faint lines with synthetic urine on a few 5 panel assay cassettes in the past. Granted, the faint lines appeared in 2 of the (off-topic) drug panels, rather than the THC panel. And we all know that synthetic urine is drug-free.