JNCIP ISIS suboptimal routing

i am facing suboptimal routing between L1 router which is R7 in my case and R3 and R4 are other extrema.

R7---R6--R5--R4
R7---R1--R2--R3

I want to ask which link should be in L1 and which would be in L2 so that i cant face suboptimal routing.

Regards,
Waqas