Cost   =   T_open  +  N_PT_P  +  NT_D

For CurveIx:

    Cost   =   2T_open  +  mT_sel  +  NfT_P  +  NfT_D

If CurveIx is to be worthwhile, we need:

    (1)   mT_sel  +  NfT_P   <   N_PT_P

    (2)   NfT_D   <   NT_D

(2) simply requires f < 1, which is essential anyway.