Correct me if i'm wrong but surely this whole subject is a "moveable feast". There is no ideal height for turning finals and it surely must never be beleived that there is.
If you are flying in "calm" condotions your height loss will be slower per "minute" than if you have a 5 kt wind or a 15 kt wind.
Is your final a 2 mile one or a half mile one?
Is you AUW near the limit or are you alone with quarter full tanks?
What a/c are you flying, a high wing "floater" or a low wing "rock"?!
Whats your HASL at your airfield, sea level or 2000ft?
Surely there can be no hard and fast rule for all these variations?
Speak to your instructor, he will explain all.