Philips 350w SON-H Mercury Retrofit: Unusual Operating Characteristics

1 x Philips 350w coated elliptical high-pressure sodium lamp for use on high-pressure mercury vapour gear.
These lamps offer increased lumen output and reduced energy consumption compared with a 400w mercury-fluorescent lamp.
The datasheet states that these lamps are supposed to run at 3.6 amps with an arc current of 117v.
The datasheet states the range of lamp voltage to be between 105 and 129v

Interestingly, this NOS lamp is operating far above that with a greatly reduced lamp current!
Granted this is a new lamp but I would not have expected it to be that much out!

Control gear is a Philips BHL400 K307 being fed exactly 240v