the only places that fences are in the way is at Quarry and Camp and Old Paddock, everywhere else is essentially clear.
IMO best opportunities are at the Esses, Bobbies, Tower, although in each case the viewpoint is quite high up. There is a good spot before the fencing at old paddock, on the exit from the esses which is at track level. there is an opportunity on the exit from Quarry, beyond the fence, and maybe before the fence on the entry, but view is limited on the entry and Quarry in general is always heaving and difficult to get a good view without people in the way.