For comparative purposes:
Stock I got about 180 us miles from a tank, putting around 5us gallons in at the pump to refil.
With my Domination tune I got around 150-160 miles a tank.
After going CES exhaust I get between 130-140 miles before a refil.
All my tune are on the richer side compared to stock, so to get under 100 miles a tank either you're ridding hard a he'll all the time, your tune is obscenely rich or a combination of the two.
As far a copying the tables for ignition over, you can do it without incident, many people have already.
Regarding the TOR tune not using much extra fuel, where you fire off the spark plug (ignition advance) has an effect on the measured AFR using a gas analyzer, and it's almost certainly the stock tune is designed to feed close to 14.7 ratio out the head so the cats work properly. With the TOR tune, Triumph would not have been concerned with the cats, and would have adjusted timing based on best power not best emissions. Also consider that best power is made across a range of afrs, not necessarily at a specific ration, particularly in low compression motors, and their tune makes sense as a "more fun but still gets descent mileage" tune.
Right off the bat, I'd wager that PowerTripp's R3T_Slip tune will work really well with a D&D bike assuming it still uses the stock header.