HowardGWR wrote "I agree, though, visually, the bits that stick out at the top, of varying heights, seem to shout 'please cut me off and make it all level'. I think our colleague Philip Phlopp explained why it is so designed, but I've already forgotten why."
Isn't it so that the autotransformer feed wire is electrically isolated from the (I hope this is the correct term) trains pantograph pick up wire, without the need to bolt on additional equipment. This keeps down the cost and makes the structures less cluttered and quicker to install. Also with ease of installation and overall costs in mind the components are made to a standard size and therefore the "bits that stick out at the top" will vary from location to location as a result of differing ground conditions, giving different top of rail to pick up wire heights?
( perhaps I should clarify what I am trying to say. I would guess that the top of rail to pick up wire distance will be pretty much constant, just that due to differing ground conditions the top of the piles will vary so to maintain this constant distance the equipment positions on the OHLE supports will vary slightly, hence the differences in the "bits left over at the top" I think I am getting out of my depth here!)