At this point in the game, in my observation, there are about two different worlds: IA and below, and Global age and above.
The majority of the highly active, long time players, and skilled player base are in CWA, or AA, and to some extent in Global age. And, all of them can attack you in your Global Age.
You might not find a sweet spot in terms of medals from Global Age and above - at least until you max out most of your defenses in Atomic Age.
Granted that with good layouts, and with a missile silo, you can minimize the frequency of attacks against your Global Age base, but, if you hold a lot of resources, you're very likely to be attacked. Till you build the missile silo, you're likely to get attacked even if you don't have a lot of resources, primarily for CWA and AA players to 5 star bases for getting their national trade goods.
Long story short, you might not find a medal sweet spot in Global age similar to how you might have found one in IA.
Hope that helps. Cheers and happy gaming!