My only concern about being seen would be in an area with heavy traffic and cars parallel-parked along the road so as to block vision of what's coming. In that case it would be wise to ride as far to the left (US) of the lane as possible. Otherwise, well, drivers hit upright riders with some regularity; so I wouldn't say that height makes you more visible. If they're looking at all, they'll see you ; if they're not...