Apart from a potential psychological advantage -- that is, the lower player may think they are disadvantaged and act more timidly -- I don't think there is much significant advantage in the situation you've described unless the players are near the limit of their effective range and you've implemented an effect where higher ground gives a range advantage.  The one notable difference is that the player at the top of the cliff is able to jump off and reach the other position, whilst the player in the canyon won't be able to jump up to reach the other player -- this isn't really relevant given the use of guns though.


In real life the advantages of higher ground include increased line-of-site, increased range, and the fact that it is more difficult to move up-hill than down or even across flat terrain.  Any of those could potentially be added into your game in some fashion.

Apart from a potential psychological advantage I don't think there is much significant advantage in the situation you've described unless the players are near the limit of their effective range and you've implemented an effect where higher ground gives a range advantage.  The one notable difference is that the player at the top of the cliff is able to jump off and reach the other position, whilst the player in the canyon won't be able to jump up to reach the other player -- this isn't really relevant given the use of guns though.


In real life the advantages of higher ground include increased line-of-site, increased range, and the fact that it is more difficult to move up-hill than down or even across flat terrain.  Any of those could potentially be added into your game in some fashion.