To answer your throttle question, yes, carb-ice is very possible at, or close to, full throttle in an R22. The reason, as you state and as others have pointed out above, is that the engine is derated and the butterfly is not wide open.
The information you add in your second post reinforces the likelihood of carb-ice. Hovering over grass can recirculate the moisture necessary to produce the ice. You state you had nil wind conditions. This just helps the recirculation process. And you'd been there for two minutes already. Perfect for ice!
I'd still get the machine checked over for all other possibles. Your 'hard' landing should be checked too if you suspect damage may have been done.
I am not a little disconcerted to read amongst the above that some of us here cannot see the likelihood of carb-ice in this case. Having done a lot of work on this subject I can assure you carb-ice in Robinsons is very possible under a surprisingly wide variety of conditions. Given that pulling out the carb-heat control costs nothing (well, almost nothing) to keep that temp needle out of the yellow arc, the rule here just has to be:::
"If in doubt, pull it out"
