Below you can see the possible positions for the 4 rotary encoder (Rev1 only 2).
If you place a encoder in the top left corner (E1), you can't use another encoder in the lower right corner.
Rev1.1 and higher Rev1
,-----------------------, ,-----------------------,
| E1 | E2 | E3 | E4 | | E1 | | | E2 |
|-----+-----+-----+-----| |-----+-----+-----+-----|
| | | | E3 | | | | | |
|-----+-----+-----+-----| |-----+-----+-----+-----|
| | | | E2 | | | | | |
|-----+-----+-----+-----| |-----+-----+-----+-----|
| | | | E1 | | | | | |
`-----------------------' `-----------------------'
KC_F17
and KC_F18
.KC_F19
and KC_F20
.KC_F21
and KC_F22
.KC_F23
and KC_F24
.The F17-F24 keys are intended to be customized via Karabiner-Elements (OSX), or AutoHotkey (WIN)