Ido,yes you need a specific height(or greater),and you can never actually obtain 100% idle,99.99% is effectively,the highest,(though it CAN go to like 99.99999999%).
I currently have the Cheater,Pillage the pet,Knowledge,Lost again,and Still Worse? secret achievements,and they're called /secret/ for a reason,ya know.
 "Anti-Idle: The Game"){kind=logo}
 "Raiden X")
 "Civilizations Wars")
 "Ring Pass Not 2")
 "Castle Carnage: Under Siege"){kind=icon}
 "Platform Journey 2")
 "The Ocarina of Time BETA 1.01")
 "A Knight's Story 2")
 "Infectonator!")
 "Perfect Balance 2")
 "A Knight's Story")
 "Frenetica")
 "Multi Tank Defense")
 "Hunter Story")