So the incandescent lamp power should always be 3.2 times more than the MV lamp?

It is indeed around that figure, but exact value depends on the arc voltage.

Because the higher power arc tend to "hold better" (less likely to extinguish), the higher power lamps are designed for higher arc voltages in order to keep the circuit current, so electrode and ballast losses and ballast cost at minimum.

This mean the multiply gets higher with higher power MVs.

On the other hand higher mains voltage at your place means there is higher voltage across the ballast and presumably you would be using higher rated voltage incandescents, it leads to somewhat higher nominal power of the incandescent as well.

I tried to better fit my model (initially I was approximating the reststance as R/Rnom = sqrt(V/Vnom); but it seems to better fit with R/Rnom = (V/Vnom)^0.43 to the

published chart)

Lamp: Ballast rating for mains voltage

MV: 120V 220V 230V 240V

50W -- 190W 196W 200W

80W -- 279W 284W 290W

125W -- 423W 429W 436W

250W -- 826W 834W 844W

400W -- 1312W 1319W 1331W

F40T12 -- 147W

F20T12 71W 105W

2xF20T12 -- 138W

F15T8 50W 65W

2xF15T8 -- 98W

F10T8 37W 58W \

2xF10T8 (80W) 73W > The "US" 0.21A shorter one (~34cm)

3xF10T8 -- 98W /

EUF10T8 34W 49W - The 0.17A longer one (~47cm)

2xEUF10T8 -- 67W - The 0.17A longer one (~47cm)

Table assumes the mains voltage and the incandescent nominal rating are the same!