How can we define iman and ihsan, and what does it mean to have both. does ihsan increase and decrease like iman

Iman is to believe in Allah, His angels, His books, His messengers, the Last Day, and the decree, its good and its bad. Ihsan is to worship Allah as if you see Him, and if you do not see Him, then He sees you. It is the highest level of the religion, so whoever has it has iman. Iman increases with obedience and decreases with sin, and ihsan has degrees: the higher is worshipping as if you see Him, and the lower is knowing that He sees you.