Something I was thinking about the game.
It becomes really easy to enter in the Top 100. Futures and Challengers are played by really low ranking players. In Real Life there´s players who spent a few years playing in those Challengers, while in every game I´ve played my main player is playing ATP by the end of the first year/Start of the second year as the most!Players ranked in the Top 100 plays Challenger sometimes.
In the other way, in TEM a lot of High ranked players plays in the ATP250.
This can be achieved by modding(just did it and tested).
In the TourCategory.Ini you need to change BestPlayer(set it lower, I put the legal minimums which are 51 for Challengers and 101 for Futures, Top 50 and Top 100 players aren't allowed to play them IRL). I also found it useful to mess with the TopPresence value to influence what events players play.
With a representative, not full schedule(meaning, not all the Challengers and Futures, just some of them each week) this isn't enough to make it look like the real tour but it is in my opinion an improvement. For example, when I did this for the first week I got DA into the 150-200 range playing 250 events, yet there were the likes of Ginepri, Sluiter, Petzchner, and Zverev(all Top 100 players) in Challengers for Noumea and Sao Paulo. The futures varied wildly, with 'full' week schedules ending up with only players in the 300s and lower, while in weeks like during the AO, guys who are just out of Slam main draw range in the low 100s(i.e., Guccione at 102) were playing futures and the Challengers had a lot of 100-150 guys. Too many, more ought to have been playing the AO qualies IMO which had a range of 175-350 as the top qualifiers elected to go play smaller events.
It's actually an interesting choice from a practical POV: as a Guccione type of guy, would you rather try to qualify(25 pts if you make it), or go to a Challenger where three wins there gets you the same or more against basically a little more diluted level of competition?
To really make this work, you need the full schedule of events -- which means you need more players -- etc. but you can fiddle with it and improve it in this way.