sabenaboy, what you have to bear in mind is that whilst the Level-Off Altitude may be a mere 300 feet lower, the last couple of hundred feet of any Drift-Down is at an extremely low Rate of Descent. This is quite normal
I've Programmed and produced Drift-Down charts for several aircraft types, and, typically, the first 10,000 to 15,000 feet of Drift-Down happens pretty fast (for 2 engined aircraft), but as the descent progresses, with decreasing Rate and Gradient of Descent, approaching zero at the Level-Off Altitude, Distance, Time, and Fuel increase for each foot of altitude lost. That last 300 feet of Drift-Down will probably be at a mean descent rate of about 30 feet per minute, decreasing to zero. Thus, although the Level-Off Altitude is lower, a lot of distance is covered for those 300 feet. If the 'Normal' table were to show you incremental Distance, Time, and Fuel between altitudes (it doesn't) you would see that the last part of the Anti Ice OFF descent also covers a considerable distance.
The increments for Total Anti Ice ON at Distance +14% : Time +13% : Fuel +15%, are nearly equal, thus, excepting a VERY small fuel penalty (+15% Vs +14%), it is more representative of a longitudinally extended Drift-Down for a slightly extended Vertical component. Very very typical of all aircraft.
Regards,
Old Smokey