How to account for M-M in the presence of Ka>Ke constraint in PopPK model

Dear NONMEM Users, I have a popPK model for which the Ka is constrained to be larger than Ke at the individual level to avoid flip-flop. The question is that if there is an additional nonlinear clearance component (M-M), how should I constrain between the absorption rate (KA) and terminal phase elimination rate (KE) since nonlinear clearance causes the KE to change with time? Is there any reference on this topic? KA and KE constraining in the absence of nonlinear clearance in NM code: KE=((K+K23+K32)-SQRT((K+K23+K32)*(K+K23+K32)-4*K*K32))/2 KA=KE+THETA(5)*EXP(ETA(3)) Thanks a lot for your input! Lei Diao Biogen