Cranksets, chain-lines and all that

The new GRX crankset supposedly has a +2.5mm chain-line relative to Ultegra, with the implication being I need to buy a new front derailleur if I want a GRX crankset.

Is this accurate?

I replaced my Di2 Ultegra crankset awhile ago with a White Industries square taper 46/30T.

Here are the chain-lines for the three cranksets:

Chain line

Shimano Ultegra 43.5 mm
Shimano GRX 46.9 mm
White industries 47.5 mm


So, two things are evident:

(1) I introduced a bigger change in chain line with my switch to the WI crankset. The Di2 Ultegra derailleur copes with this just fine, so presumably a Shimano crank with a slightly smaller difference in chain line would be even less problematic.

(2) 46.9 - 43.5 mm = 3.4mm, not 2.5. WTF?