While not the biggest elephant exhibit I've seen, it's plenty big enough. Compare the apparent sizes of the elephants in fore- and background for an indication of the depth of the paddock. And remember that (as with almost every photo you've commented on) you can't see the whole exhibit here.
Lowry Park Zoo has had impala in with its African elephants for a number of years, and Dallas Zoo does the exact same thing plus there are additional species there as well. I know that Birmingham Zoo has considered the idea of mixing antelope (possibly impala) with its 4 male African elephants and so far I've not heard of any issues at these zoos. I agree with your thoughts in terms of the riskiness but it seems to be working.
Lowry Park Zoo has had impala in with its African elephants for a number of years, and Dallas Zoo does the exact same thing plus there are additional species there as well. I know that Birmingham Zoo has considered the idea of mixing antelope (possibly impala) with its 4 male African elephants and so far I've not heard of any issues at these zoos. I agree with your thoughts in terms of the riskiness but it seems to be working.
It seems to actually always come down to the individual temperament of the dangerous animal involved in mixed exhibits. I am thinking its very dangerous to say it worked well at zoo A so it will work here at zoo B. I know of many cases were primates have been killed in so called compatible mixed exhibits!
I know I'm a bit late to the party and this was probably not the case at the time these comments were made but Magdeburg Zoo in Germany also mixes Impala with their elephants.