This is my feeling. Doubling up wattage at that point is worth a measly 3dB. Something is up in the amp gain or your cabs are miswired or plonked 3 to 8ft from a corner.
The Streamliner is a nice, loud, full sounding amp. However, it uses complex power management to reach its wattage rating, which some of the tech guys still dispute.
With most cabs and for most users, it just pumps, and is full and loud. However, when I did some A-B testing between the Streamliner and the M6 into an 8ohm fEARful 15/6, there was actually no contest... the M6 WUMPED it. I think the combination of the deep low end capability of the fEARful cabs, combined with moderate sensitivity, and the rather sharp hi passing of the Streamliner with its 'non traditional' design results in it not quite performing as you would expect with the fEARful cabs, given its nominal power rating.
And, additional wattage is often not about volume, but about deep, uncompressed, low end headroom. If any cab is capable of laying any low end performance issue of an amp bare, it would be the fEARfuls (or even more so, the Acme's).
Not doggin' the Streamliner... love it! But if you are playing stupid loud, I can see running out of deep, uncompressed low end as that power management system kicks in. To me, that actually sounds quite good if you are going after a vintage vibe, since it emulates the way an all tube amp breaks up and compresses when pushed quite nicely.
That being said, and to your point (and to the OP), if you are running the amp with those gain and master setting, your 'power management/clip' indicator should literally stay on constantly. If it is not, there is something wrong with the amp.
IMO and IME.