Looking at the joystick reading code in Gumball,

finding it by watching reads from c065 (paddle1)

wp c065,1,r

This leads to the reading routine at 69d8:
Code
 69D8  lda #$00                                            A9 00
 69DA  sta $e5                                             85 E5
 69DC  sta <HGR.PAGE                                       85 E6
 69DE  lda PTRIG                                           AD 70 C0
 69E1  ldx #$01                                            A2 01
 69E3  lda $c064, x                                        BD 64 C0
 69E6  bpl $69fb                                           10 13
 69E8  inc $e5, x                                          F6 E5
 69EA  dex                                                 CA
 69EB  bpl $69e3                                           10 F6
 69ED  lda PADDL0                                          AD 64 C0
 69F0  ora PADDL1                                          0D 65 C0
 69F3  bpl $69fe                                           10 09
 69F5  lda $e5                                             A5 E5
 69F7  ora $e6                                             05 E6
 69F9  bpl $69e1                                           10 E6
 69FB  nop                                                 EA
 69FC  bpl $69ea                                           10 EC
 69FE  lda $e8                                             A5 E8
 6A00  bpl $6a0d                                           10 0B
 6A02  lda #$3f                                            A9 3F
 6A04  sec                                                 38
 6A05  sbc $e5                                             E5 E5
 6A07  bpl $6a0b                                           10 02
 6A09  lda #$00                                            A9 00
 6A0B  sta $e5                                             85 E5
 6A0D  lda $e9                                             A5 E9
 6A0F  bpl $6a1c                                           10 0B
 6A11  lda #$46                                            A9 46
 6A13  sec                                                 38
 6A14  sbc $e6                                             E5 E6
 6A16  bpl $6a1a                                           10 02
 6A18  lda #$00                                            A9 00
 6A1A  sta <HGR.PAGE                                       85 E6
 6A1C  rts                                                 60

Code
 6EC4  jsr $69d8                                           20 D8 69
 6EC7  lda <HGR.PAGE                                       A5 E6
 6EC9  cmp #$0c                                            C9 0C
 6ECB  bcc $6ed4                                           90 07
 6ECD  cmp #$38                                            C9 38              <<< compares to 38
 6ECF  bcc $6f17                                           90 46


So if I put a breakpoint to show the values being returned:

bp 6a1c,1,{printf "e5=%x e6=%x",b@e5,b@e6;g}


maximum e5 value is 34 (joystick x)

x max, y centered
e5=34 e6=1B
e5=34 e6=1B


maximum e6 value is 35 (joystick y)

x centered, y max
e5=1A e6=35
e5=1A e6=35


Now If I patch the comparison to 35 then the joystick down works

6ECD cmp #$38 C9 38 <<< compares to 38


6ECD cmp #$35 C9 38 <<< compares to 35 now the joystick y down works