While OS' answer may be simplifying some points for convenience ... seems I'm missing something here on a couple of points ...
As Elevation (1000 ft) is quoted for the highest part of the airfield
When one is doing the sums .. other than in a quick and dirty manner to get a conservative answer .. calculations usually are based on the specific MSL RLs quoted in the aerodrome runway and relevant terrain data. Assuming one has this data .. the end elevation/obstacle RL deltas on which the sums are based are then simple differences of values measured from a common datum. Indeed, if one has the actual centreline RL profile then one can be a little cleverer and determine the (approximate) actual RL at end TODR rather than use the end TODA declared figure (or use a somewhat conjectural linearised approximation) if the TODR << TODA.
The ARH is of little direct relevance (although, for convenience, the ARH may well be input as the Hp argument if one is doing the sum manually). If one is going to the trouble of using a number cruncher, then one would input an appropriate RL for the sake of a poofteenth improvement in "accuracy".
If the elevations quoted are MSL RLs, then I have missed something along the way in the leap as to how obstacles are referenced to the lowest portion of the runway.
For the two (opposite direction) examples given, each is quite separate from the other and the lowest portion of the runway appears only to have relevance to the departure in the downsloping direction ?
Answer (2) appears not to be related to the wordiology of the question in respect of will begin at a relatively LOWER elevation relative to a downhill slope runway.
Perhaps it is just a bit late at night and I am overlooking something specific in the wordiology ? Alternatively, having been involved in pilot theory training in another lifetime and having a fairly jaundiced view of Regulatory examination questions .. especially the lack of lucidity relating thereto on many occasions ...... If I may relate an anecdote at my expense .. many years ago .. as a recent graduate I undertook my Oz ATPL exams by my own study .. read the syllabus for each topic .. read the nominated texts .. and then, in the exam, managed to complete the "enter-your-name-in-this-space" question but precious little else. I then found out about past sample papers and the fact that the exams had only a passing relevance to the required subject academic competence ...
signed,
Confused