Winky,
You are not being rational. You are still laying the same wood in a parlay as a straight bet. In fact you probably lay more wood this way because your line shopping possibilities are restricted.
If your bet has a positive EV it should be made as a straight bet. If it is negative or zero it should not be made at all.
Please tell me: do you think TB-185 has a positive EV or not?
Thanks.