In short, this partial (or harmonic, as it is sometimes called), is flat on most brass instruments.
In 1st position, the Ab will sound flat because the tubing isn’t quite short enough for that note to be in tune and when you’re in 1st position, it’s not possible to make the tubing any shorter….EXCEPT if you tune your instrument to be slightly sharp!  But the trade-off of being able to play that Ab in 1st position is you’ll need to play all other 1st position notes slightly further out than the closed position.  But I digress.
To play the high G in tune, we need to position the slide slightly further in than 2nd position.  The same is the case for F#.  It will need to be played in a short 3rd position, and so forth.
The alternative is to simply play that G in 4th position.  This is what valved instruments must do (by playing it with 1st and 2nd valve rather than using 2nd valve only).