E vs A country (mixolydian) thirds — B (2nd) & G (3rd) strings

Flat-7 scales — the country sound. Most shapes transfer directly between E and A. Only two pairs actually differ.

E country only

A country only

Shared by both

Root

The shortcut: with the flat-7 (mixolydian), the only note that differs between E country and A country is G# (E's 3rd) vs G (A's b7). Everywhere else the scales agree. So 5 of your 7 third-shapes on strings 2 & 3 are identical between the two keys — memorize once, use in both.

Scales

E country (E mixolydian) = E F# G# A B C# D
A country (A mixolydian) = A B C# D E F# G
The single note of difference is G# (in E, not A) vs G (in A, not E).

Diatonic thirds on strings 3 (G) & 2 (B)

Pair (low → high)	Interval	G-string fret	B-string fret	Shape	In E?	In A?
A–C#	major 3rd	2 / 14	2 / 14	same fret	yes	yes
B–D	minor 3rd	4	3	split (G higher)	yes	yes
C#–E	minor 3rd	6	5	split (G higher)	yes	yes
D–F#	major 3rd	7	7	same fret	yes	yes
F#–A	minor 3rd	11	10	split (G higher)	yes	yes
E–G#	major 3rd	9	9	same fret	yes (E only)	—
E–G	minor 3rd	9	8	split (G higher)	—	yes (A only)
G#–B	minor 3rd	1 / 13	0 / 12	split (G higher)	yes (E only)	—
G–B	major 3rd	0 / 12	0 / 12	same fret	—	yes (A only)

Where the two keys actually differ

Two fret regions. Everything else is the same.

Around fret 9 (the E position):
• E country: E–G# on fret 9 of both strings — same-fret major 3rd.
• A country: E–G on G:9 / B:8 — split minor 3rd.
Same root note (E), different upper note, different shape.

Around the nut / fret 12 (the open position):
• E country: G#–B on G:1 / B:0 (or G:13 / B:12) — split minor 3rd.
• A country: G–B on open/open (or fret 12 / 12) — same-fret major 3rd.

Pattern to hear: the two "flip" pairs always swap shapes. If a shape is "same-fret" in E, it's "split" in A at that same scale position — and vice versa. That's literally the one-note difference (G# ↔ G) expressing itself as a shape change.