[GZG] Threshold question using Beta fighter rules

Am playing a series of fleet exercises (i.e.better familiarizing myself with
the beta fighter rules) and have a question on Threshold damage modifier. The
situation:a group of 4 surviving heavy fighters is attacking a NAC
Troutbridge-class frigate (hull 2/1/1/1) that has already lost first row
of hull boxes (3 remaining);one fighter out of the group rolls a beam die of
"6" for 2 points damage on its attack run,thus causing Threshold check to the
frigate for losing second and third rows of hull boxes. FB1,p.5 states "If a
ship suffers enough damage in a single attack to push it past one Threshold
check,make only one check (for last row destroyed) but add 1 to each die roll
for extra Threshold point passed in that attack."
So do I check Threshold at 4-6,or is it now 3-6 per system?
I am interpreting it as 3-6 per system due to going past 2 rows damage
at once,but want to make sure I am reading it correctly.Never have been too

clear on this point.......

BTW,if anyone is interested in how I am conducting the exercise I can post it
here in scenario format.

Thanks,

From: "Mark & Staci Drake"
> Threshold check to

You're doing it right--the frigate loses systems on 3-6.