Big figs and Barriers

[Thunderbolts]

Can a Sentinel or Sinestro be protected by a Barrier, or can it just be seen above the barrier in the same way that normal sized figs don't block sight to a big fig?

[HeroComplex]

Unless an exception is specifically and explicitly stated in the Sentinel/Sinestro documents, the same LOF rules apply to the big fig as would to any normal figure. Blocking terrain blocks LOF.