Can I ask what your test out numbers average?
on one job, the guys bragged that they used 8 gallons of mastic.
(HO bought through Home Depot...need I say more?) the amount of duct leakage
was reduced from 300 cfm...to 200 cfm. but there were gobs of mastic all over
the place..they filled in the top of the sheet metal plenums...but not where the top
of the plenum attached to the sides..you know where the joint is! ha ha ha.
my advantage is that I test the ducts before and after sealing them.
not to bash the hvac industry...the job is to get it installed & running.
ducts are secondary for most.
just my pov