What Hood For Low Ceiling And How Far Should 125mm Round Duct Pipe Be From Wall?

Ian would like to know the answer to the following question, if you have a suggestion then please post a reply:
The available height above the hob is 1290, I am installing a duct in the ceiling in a barn conversion and need to know if there is a standard distance from the kitchen wall for the 125mm opening in the ceiling as I am about board it over. I have also noticed that some hoods say not suitable for radiant hobs which is a concern.