Mathematical odds of winning an mtt with a given ROI?

[DMACM]

My question is how from a theoretical perspective does ROI interact with odds of winning an mtt and further how does the size of the field interact with these numbers.

I understand that this is probably a difficult question from a theory stand point but is there a generally accepted shorthand way of determining your odds of winning a tournament assuming a given ROI?

I ask this because I generally like to take the size of the field/2 as my odds of winning a tournament but I have been realizing lately that this is probably incorrect.

To complicate things further I would assume that in a larger field an average player has a magnified chance of winning as compared to a poor player. If this is the case would a fantastic player have a magnified chance of winning compared to an above average player?

This is of particular relevance to the large sunday events and the WSOP. Both of these have a lot of above average players probalby play and to whom winning such an event would represent a drastic change in the overall profitability of their poker careers, many who perhaps play them only occasionally and outside of their bankroll. Both of these also attract the best of the online pros and live pros.