A month ago, Juan Soto was having the same season in 2019 that he did in 2018. And that would have been amazing enough on its own, even historic, when you throw in that he's only 20 years old.

But he's not having the same season anymore. He's having a better season. Here's what's happening.

Let's start with what's the same type of mirror-image exercise from August: 2018 Soto vs. 2019 Soto.

Offensive output
2018: .292 BA | .406 OBP | 145 wRC+
2019: .295 BA | .404 OBP | 148 wRC+

Plate discipline
2018: 16.0% BB | 20.0% K | 22.2% whiff | 18.3% chase
2019: 15.2% BB | 20.0% K | 23.7% whiff | 20.7% chase

Spray chart
2018: 32.6% pull | 40.5% straightaway | 26.9% oppo
2019: 34.7% pull | 38.1% straightaway | 27.2% oppo

Those are a whole bunch of key stats within a few percentage points of one another. With those stats, Soto was a great hitter last year, and with those stats, he's a great hitter this year.

But something did change. You might notice the third slash line category missing from the top group of stats. The slugging.

At the beginning of August, Soto's 2019 slugging percentage was within a handful of points of last year (.524 vs. .517), and he had 20 homers. Fast-forward to September ... He's slugging .576. He has 33 home runs. He's only played 16 more games this year than last year, but he's added 11 extra homers.

So how's he doing it?

Soto found the sweet spot

To slug is bipartite: You need the exit velocity, and the launch angle.

The exit velocity threshold the hitter wants to meet is 95+ mph -- that's a hard-hit ball, by Statcast's definition. The launch angle window to target is 8-32 degrees -- that's what Statcast defines as the sweet spot, because it spans the best range for base hits (8-16 degrees) and home runs (24-32 degrees). Meeting one of those criteria is good; meeting both is ideal.

This season, about 200 hitters have put at least 250 balls in play. Guess who's hitting it hard and in the sweet spot the most?

Highest hard-hit + sweet spot rate, 2019
Min. 250 batted balls (197 hitters)
1) Juan Soto (WSH): 26.4%
2) J.D. Martinez (BOS): 26.3%
3) Matt Olson (OAK): 25.7%
4-T) Josh Donaldson (ATL): 25.4%
4-T) Nelson Cruz (MIN): 25.4%
Hard-hit: 95+ mph. Sweet spot: 8-32 degrees.

More than one out of every four balls Soto hits is in that happy hard-hit/sweet-spot place. Last season? Only 18.4% of his batted balls were both hard-hit and in the sweet spot, right in the middle of the pack of Major Leaguers. This is a dramatic improvement.

Fly balls and line drives, obviously, are what get you extra-base hits. (That's why Daniel Murphy calls ground balls "seven-percenters.") But you also have to hit hard fly balls and line drives.

Here's another way to look at it: On a season-total basis Soto is in the Top 10 in MLB, and in the Top 5 in the NL, in hard-hit air contact (as in, fly balls and line drives). He's right up there with his MVP candidate teammate, Anthony Rendon, and the other elite sluggers in the league.

Most hard-hit line drives/fly balls, NL hitters
1-T) Freddie Freeman (ATL): 146
1-T) Cody Bellinger (LAD): 146
3) Anthony Rendon (WSH): 138
4) Ronald Acuna Jr. (ATL): 135
5) Juan Soto (WSH): 129
Hard-hit: 95+ mph exit velocity

Soto getting a lot better at the intersection of hard-hit contact and air contact is no surprise when you look at what he's done in each of the component parts.

Soto is launching the baseball

Soto's air contact has increased dramatically. His average launch angle has increased from 5.5 degrees in 2018 to 12.1 degrees in '19. His line drive and fly ball rates are up dramatically. He's slashed his ground balls.

So when you look at his batted ball profile, the 2018/2019 mirror-image exercise doesn't work anymore.

2018: 54.7% ground | 40.2% air (19.0% FB + 21.2% LD)
2019: 42.4% ground | 53.9% air (26.9% FB + 26.9% LD)

Last year, for all his 19-year-old brilliance, Soto hit a ton of grounders. Not so this season. Nearly 54% of Soto's batted balls have been fly balls and line drives. He's making more air contact than three out of four big leaguers. He's basically flip-flopped the amount of balls he hits on the ground and the amount he drives in the air.

Soto is ripping the baseball

On top of lifting the ball more, Soto is hitting the ball harder than he did as a rookie, too. His average exit velocity, hard-hit rate and barrel rate -- that's how often he hits the ball with optimal exit velocity and launch angle, producing the level of contact that gets you homers and extra-base hits -- are all up significantly.

So when it comes to Soto's quality of contact, the mirror image fails again.

2018: 89.4 mph EV | 42.2% hard-hit | 9.8% barrels
2019: 91.0 mph EV | 47.2% hard-hit | 12.5% barrels

Soto seems to have pulled off what every hitter dreams of. He's kept all of his contact and on-base ability, and added power. He hasn't abandoned the approach that star-struck fans a year ago. He's done this at an absurdly young age.

If what he was doing before was already historic ¡­ Well, what do we call it now?