Some explanation then on what goes on in my head
When I talk about Shields in the DRv3 article, I mention that shields are usually one step better than the power armors using it. Usually shields aren't as thin as the armor you're wearing; it's probably a much denser plate that you have some faith will be able to take damage would wouldn't be able to. For example, the Daisy - currently listed as a Medium Power Armor (Tier 5) - would usually have a zesuaium shield that would soak damage just as well as a Heavy Armor target.
At which point, in my head, I'm counting that as "tier 5 native +1 for being a shield"; summed up as Tier 6 as long as people get why.
So, when I look at the best shield an infantryman might lug along, that heavy personnel's +1... so 3+1. But then I consider that shield in the same light as some big squad assault weapon that's really heavy to carry around. After all, the next best shield is a heavy plate of metal only a light power armor with assisted strength could carry on one arm. So, I figure that going one step down - the native shield for medium anti-personnel - is the kind you'd be able to carry on one arm just like you can hold a rifle in one hand (firing well with it is a different matter altogether, but that's beyond the scope of this topic). So, I figure, being Tier 2+1 is probably pretty good for that shield. Sure, going Tier 3+1 would be 'more resilient', but it would also be 'different', so for this project going for
more might not be
better.
And it leave the room to allow the solid volumetric to upgrade it without going so far as to step on the toes of the super heavy plates power armor use as shields. It lets it go from "tier 2 native +1 for being a shield" to "tier 3 native +1 for being a shield" without the implied weight of a shield native to the heavy personnel category. You could have this ID-SOL with a huge heavy shield next to you, and achieve being able to block attacks coming from an LASR with a lighter shield enhanced with Origin tech.
Something which, to me, sounds like a pretty sweet deal - you could have this one guy cover his entire team from some pirate power armor hosing them down with an LASR. Your shield is probably going to eventually perforate under the prolonged abuse of a high rate-of-fire weapon like that, but while it lasts, it's pretty awesome.
That's where I come from, anyways.