>>BTW some modern boxes, Mercs for one, are actually more economical than manual ones, I believe

I expect some drivers will achieve better economy with an auto, due to their driving style. I reckon an economy minded driver will always achieve better economy with a manual.

Anyway, you can't coast an auto. ;>)

You need to find the change points as autos are programmed to keep the car at a compromise between the best point gear for car control and economy. If they changed up too early when you want to accelerate the car will need to change down. MPG differences are largely down to the torque convertor on traditional autos.

On my X type if I drive at an indicated 30mph it's in 3rd, increase this to 32 (which is actually 30) it changes to 4th, but it does cause it to hunt slightly as if I drop to 29 it drops a gear - at times when I know I'll be slowing I keep to 30 and stay in 3rd. At quieter times when I can maintain 30ish longer I'll increase speed slightly to get it to change to 4th and maintain 30 in 4th gear. 3rd is better when I need to accelerate as no change down is required. 30mph in 3rd is just about 1600 rpm - ideal revs to benefit from the torque of the car, the next change comes at just below 2,000 rpm dropping back to 1500 with the next gear.

It's a similar situation around the 60 mark - get it to about 62 and it will change to 6th gear from 5th and be at about 1500 rpm.

I've had Audi DSGs and mpg is equal/better than manuals, but they don't change to top gear until 50+ mph which puts to bed the myth that high gear at low speeds results in better fuel economy.