Robin, your second suggestion is the right one I think.
The player's mentality will determine his starting position with regards to his actual position (eg. an MC with an attacking mentality will stand on the pitch in a more advanced position than an MC with a defensive mentality). The Fowards runs option will then determine how often the player makes a run forward from that starting position (eg. rare forward runs - holds his position, often forward runs - often makes a run past a marker into advanced positions).
Hope that helps.