RomRaider

I just recently built a brand new engine for my '04 FXT (forged pistons, equal length header, up-pipe, down-pipe, full Invidia exhaust, GrimmSpeed BB500 Turbo, DeatschWerks 850cc side feed injectors).

Upon installing the new engine, I reflashed the ECU with a bone stock ROM (I'm using Romraider and ECU Flash) to have a clean start because so much had changed since the engine swap (before it just had a VF39 turbo and Invidia downpipe on a high milage motor, everything else was stock).

I'm not completely new to tuning, as I've tuned several of my own vehicles in the past.

The weird thing I'm running into with the injector scaling is that I'm having to set the scaling number in Romraider close to 650cc to get the highway cruise 3000-ish RPM fuel trims within a few percent of zero... That seems quite a long way off from what these injectors are supposed to be, which is 850cc. If these were some no-name brand injectors I might suspect I received smaller injectors than I ordered, but DeatschWerks is supposed to be a good reputable company for injectors.

Is it normal for the injector scaler to be so far off from the expected injector size?

Yes, that is normal, if you increase your fuel pressure you would need to increase the flow rate. I am running ID1300cc injectors but the flow rate at 43.5psi is 1240ish but yes its normal.
If your injector data is right you will not have variables at idle part throttle and wot. If you changed your bore and stroke you will need to rescale your MAF then try again. (new engine displacement / old displacement = Maf scale change.) so mine is 2.356/2.0=1.17

I don't know if you changed the piston bore but that you need to account for Bore x Stroke = displacement To calculate the displacement of an engine, you can use the formula: \(Displacement=\pi \times (bore/2)^{2}\times stroke\times numberofcylinders\)
or just find an online Engine Displacement Calculator.

I have the same Turbo, I think they cut corners with the wastegate flapper or the bushing cause within a few months I was having to readjust the wastegate and within a year I was welding the internal gate and installing a external wastegate.
I went IAG closed deck with JE 100mm hybrid forged pistons and Manley H-Tuff 75mm rods with Ej205 Crank stage 1 IAG oil pump and ported and poted bowls and installed bronze guides with manley exhaust valves and IAG valve springs and titanium retainers good for 8k rpm I think it was like 86lb seat and 196 open or 200 open I cant remember.