Ohh!
Let me try staying close to the portal then :D
There is no indication that being further away from the portal makes the game harder but that would help a lot!
Maybe some kind of slider with the danger icon on top (eg. Elite Monsters in WoW have that dragon frame)?
Edit.
Ok staying close to the portal made me realise one more thing.
Since there is no background I did not know I am moving slower backwards. (that is was was killing me)