Putting the radar on the mast has several effects:- (1)It increases the chafe on the leech of the jib. (2)It puts more weight higher up, so it reduces your stability (3)It increases the extent of sea clutter (4)It slightly increases the distance to the radar horizon (5)It means you get to pay more when you need the magnetron replacing.
The aft pole idea is often accused of causing radiation problems --- but if you actually do the calculation, then you find that resting your head against the radome of a typical yacht radar while it is transmitting is likely to produces less damage to you than using a mobile phone.
Thanks. Reading all the responses on this forum and the YM forum and discussing the subject with several other boat owners I decided to put the radome on a pool. Exactly for the reasons you mentioned.