APU:-
Carb heating regimens are so specific to aircraft/engine type that I'd hesitate to offer you advice about a Rotax 912. As a general rule, though, I shouldn't have thought that there was ever a good argument for using partial carb heat in any regimen. And if you've taken action to ensure your carburettor is ice-free before beginning the take-off roll, there's no reason to accept the power loss involved in keeping it on all the way through.
That said, if there were a recipe for building up as much carb ice as quickly as possible, it would look something like this:-
1. Operate an O-200, perhaps the most efficient carb ice generator ever designed.
2. Run it for a good while at low RPM, e.g. during a long taxy...
3. ...with the relative humidity at or near 100%, and OAT in the -3C to +16C range...
4. ...over wet grass, with lots of water droplets that can be easily sucked up.
I wonder whether that's what happened here. EIBR is a grass field, and the local news reports said that it had been recently raining.
This much I know for certain. O-200-powered C150s ice up like you wouldn't believe, especially in the kind of (relatively) warm and moist conditions found in northwestern Europe. When they do, the symptoms do not always match the stereotypical "cruise pattern" of a steadily decreasing RPM over a long time followed by rough running. Sometimes the ice build-up occurs within seconds, not minutes. Sometimes you get a huge RPM drop and associated spluttering without any prior warning at all. Sometimes the engine just stops. I lived in eastern England for a while and used to fly a decrepit C150 from an even more decrepit grass strip. In the kind of conditions prevailing at EIBR last Sunday, it would ice up so badly that we couldn't taxy from one end of the field to the other without the use of carb heat. We'd go over a bump; the engine would die; and we'd be left sitting there for five minutes until it melted and we could re-start and have another try. That taught me everything I needed to know about O-200s and icing (and the same manufacturer's O-300, which is nearly as bad) right there.
When flying C150s --and I now own one -- I am religious about carb ice prevention: before take-off; in the cruise; and on final approach. Given the appalling number of recorded stoppages due to induction icing with this type of aircraft, there's absolutely no reason not to be. It's a known killer, and a completely preventable one.