Tend to just get the black smoke at high revs usually, not something associated with econonmy driving!
I get 400-430 miles per tank usually, that's from full (without venting) to the reserve light/beep. I only drive 7 miles each way to work/back, but do so at funny times in the morning so need the car. Some mornings I average 6mph avg speed, which don't
help I don't drive on reserve for long if I can
help it - the remaining range tends to alarm me when its reading 25 one minute 0 the next cause I went round a corner!
Usually though, fill car once a month, £50, that sorts me out.
Last tank I put in Shell VMax power stuff whatever it is. Can't say it's better on fuel but it does seem to be slightly more responsive with the right foot. I wondered what it was until I remembered the fuel I'd used rather than normal shell stuff.