DB - I have been watching pilots perform in the 139 sim for more than 10 years and I can tell you that if you want to guarantee misselection of AP modes under IMC conditions in an MP environment then get the PF to make them. If the PIC wants to effectively manage the situational awareness then I suggest he act as PM. That way he gets to be a more effective manager of the situation and make the AP selections whilst vetting all that the PF does.
We have just written the 139 FCOM for offshore and so this is a very active area of discussion.
G
PS - I wouldn't rule out the flat cross-cockpit gradient as a factor. BTW you can move the HDG bug using cyclic trim in the 139 so maybe a better system than that on the S92.