ASSET Standard macrocell model (K's)

[justdream]

My friends, is there any restrictions regarding changing K5 (-13.82) and K6 (-6.55) in ASSET Standard macrocell model,
I noticed that changed one or both of them help me in enhance my coverage, i'm sure that K3 and K4 are constants, but what about K5 and K6?

Also guys, do you have logical values of K1 and K2 for macrocell model?

Hint: all this discussion is about UMTS