I haven't tested this in the IX, but the data in the chart is for a later IX with the rear tanks (an additional 75 gallons ~).
For the IX we have the range is considerable shorter when running with those settings. I believe we only have the forward tanks in the IX, which gives a capacity of between 75-85 gallons.
For cruising and range you should be running more like +4lbs and whatever RPM you need to obtain 170-180mph to a minimum of 1800RPM. If you need less than 1800 RPM reduce manifold until you hold that speed at 1850-1900 RPM. This should also be run on lean mixture and not rich.
This should give you about an hour and half of flying, Maybe if you are pretty good with trimming etc you may get up to 2 hours (giving you somewhere in the region of 300miles range, circa 500km.)
Like I said I haven't tried it in sim, but this is how the RL maths stacks.
Pman