4.4kg/mm front, 5.3 kg/mm rear

You'd hafta ask Eibach!
For me, I take it as roughly "a lot stiffer"...

I should mention that mid-corner understeer was reduced with the stiffer swaybars, but I'd still like a bit less and for the car to be more pointable. Just don't know how far I can go redistributing front/rear roll stiffness before unloading of the inside rear becomes an issue for the Torsen. Especially given the car's unfortunate nose-heaviness...

Gotcha

I see. I believe for our platform aftermarket ARB manufacturers typically use the 14 mm '13–'16 / non-PP OEM bars as a reference.

If my math and parameters are right, your car has higher front/rear roll stiffness ratio than any stock BRZ/86/FR-S, making it naturally pushy.
To match the front/real roll stiffness ratio of the '13–'16 BRZ you'd need a bar that's 250% stiffer than the 14 mm OEM.
You can probably go even stiffer, maybe up to 300% stiffer than OEM.

That's a valid concern.
Depending on your goals and the budget it might be worth investing into a clutch-type LSD to address this, to "unlock" more possibilities to achieve the desired balance in the first half of the corner.

Front/rear spring rates are slightly more rear-stiffness biased on my car vs. stock BRZ.
No stock factory BRZ/86/FR-S had -3.5 front camber, that does make a bit of difference in "pushiness"...

That's not an approach I'm going to take due to 1) daily street car and 2) sway bar rates are already quite high relative to springs and dampers (Bilstein B8).
I might swap the stock front sway bar back in.
Or not... Car is quite driveable and capable of decent lap times as it is.

Yeah, I'm considering that. But $$$$...

Ultimately I'd like to cut out a section of the car between the rear wheels and the doors to fix the weight distribution. Not exactly a practical solution tho!

I understand. I'm calculating the overall roll stiffness (springs+bars), not either of the components individually.

True.
I'm calculating only the stiffness of the suspension, not factoring in the effects of alignment, camber curves, etc.
They can be accounted for separately, but I'm not doing that right now.

If my math is correct and you keep the +150% rear bar, but stock front bar, the car will be way too loose.
More loose than any suspension setup I currently have in my spreadsheet.
I suggest trying a ~+100% over stock front bar instead, such as Perrin 19 mm on the Hard setting, or Whiteline 20 mm on Soft, or Perrin 22 mm on Soft (these three provided options are in the softer-to-stiffer order).

I shall request a restraining order to make sure you can't be within a 1 mile radius from my car :D

So what's the point apart from the fact that you didn't have a better time with the reverse stager setup and that the lap times can have a variation from day to day? Maybe it can be easier to get a repeatable result in some of the Nascar type tracks you are going on same day, but again there are additional variations if you are timing on different days.

I did do a better time on Sunday with reverse stagger 245/40-17 fronts and 235/45-17 rears, vs. 245-square. See my best 235/245 reverse-stagger (brown) vs. best 245-square (purple) Sunday laps below.

Not really a "Nascar type track". NHMS for road racing goes outside the oval and has elevation changes. In this configuration (South Oval) uses one of the oval turns and one and a half of the straights. But it's a lot more similar to "normal" natural terrain road courses than to driving the oval.

For sure there are day to day variations, but it definitely looks like on Saturday I was doing a better job carrying speed into turns 3, 6, and 9.
See the bottom plot for my best lap on 245-square from Saturday (green) and from Sunday (purple). Actually, looks like time lost in 9 on Sunday was immediately gained back so call that a wash. Big differences are Turn 3 and Turn 6 where, lost 0.25s in each of those. It is a subtle art and consistency is not one of my strong points....