Ok, so I've been pondering this and think I've come up with a relatively simple explanation of the driving modes and why they are better for certain scenarios.
Prioritizes ev bursts, it doesn't build up the battery for sustained drives.
Best for stop and go/ traffic/ city. To achieve best results, coast as much as possible up to red lights/traffic.
The balanced approach. Depending on speed, engine load etc, this drive mode has the widest range of applications and computer input. On slower drives Normal mode will try to maintain 4+ bars of battery, but with enough traffic, will sometimes allow down to 2 bars of battery. On faster drives (45+) on flat highways, I've regularly seen this mode build up to 8 bars of battery and then run EV only until 4 bars. Rinse and repeat. It sustains EV only for a mile+ at time resulting in better highway mpg.
Best for Highway driving, and generally any time you will sustain a speed of 30+mph for any time longer than a minute or two.
This is not meant to be a fuel efficient mode, but a more aggressive mode. Under certain conditions, it can actually be the most efficient mode. (ie. Rolling hills). This mode prioritizes battery reserve, and unless at a set speed, or near full battery it rarely chooses to run EV only. The thing to remember here, is that if you are in a situation where the ICE would be running anyways. Terrain, drivetrain load etc... This is the go to mode, because every chance that it gets, the computer will charge the battery pack.
The thing we all have to consider is that battery percentage directly correlates to fuel efficiency. If we have the opportunity to choose a route with a long descent over a shorter steeper descent, up until the point where the battery pack would be at a full charge, the longer descent wins. If we have the opportunity to take a slightly longer route, with less traffic/stop signs etc. that will always be the more fuel efficient route (with similar topography). If you know you are on a flat section, or descent, leading up to an incline, shifting to sport mode to build the battery charge will result in better overall fuel efficiency.
When we first got the car, it lived in Eco mode, but now after a couple months of exploration and observations, I actually swap modes accordingly, and have noticed better fuel efficiency. This may not be necessary for those that aren't "topography challenged" but for those of us where every commute involves climbs and descents, it's still possible to beat EPA mileage, albeit it a little more of a conscious effort.