3rd ?

Interesting question.

You're right, if you use the slide to create the same scale pattern for the key in each position, they should both sound fine.

Slight correction: By hole in second position the scale would go 3+ 3'  4+  4+'  5  6   7+.

That is, if you always play single notes. As soon as you start playing chords, the third position draw chord will fit the minor character of the tune, while the draw chord in second position will clash.

One of the great things about third position on chromatic is that the minor home chord of the key is everywhere throughout the entire range the harp as a draw chord. If you play a tongue slap or let neighboring holes bleed in with your single notes, there's agood chance that those added notes will fit with the background chords.

However, in second positoin on a chromatic, the draw chord contains the one note that makes it a major chord, and major chords nearly always sound bad against a minor background. So slaps, bleeds, etc. stand a strong chance of clashing, like bright orange socks with a black tuxedo.

Let's look a little closer at the blues scale in second position, though.

It's worth noting that the second-position blues scale contains two choice notes -notes that can be played as either blow notes or draw notes by using slide-in alternate versions. So when you play the 4th degree of the scale, 4' can replace 4+, When you play the flat 7 degree of the scale, 5+' can replace 5.

Let's look at the harp as two breath planes:

-- The blow plane, containing all the blow notes, both those played with the slide out and those played with the slide in.

-- The draw plane, containing all the draw notes, again including both slide-out notes and slide-in notes.

The scond position blues scales lays out like this:

BLOW PLANE: 1+ 2+' 3+ 4+ 4+' (also 5+ and 5+'), and so on. The only "avoid note is BLow 2 (or 5) with the slide out.

DRAW PLANE: 1 2 3' 4' 5, etc. The only avoid note is Draw 4 with the slide out.

All of the slide-in notes can be approached below with a slide jab, starting with the slide out and then jabbing it in to arrive at the target note - sort of like the slide version of a tongue slap.

Now, let's say you spend some time with your note choices hard-wired to the ones I just described.  Play them up and down as a scale, but also do this:

-- Explore using only the notes on the blow plane, making sure to stick to the notes in the scale.

-- Explore using only the draw notes, with jabs allowable for the flat-3 and the slide-in 4.

By doing these things, you get used to sticking to a pure blues scale in second position, both expanding your possible moves (and along with them, melodic material including licks and riffs) and giving you confidence playing that position in a pure minor setting despite the prsence of a major chord.