I've found "TKO Boxing (VS)" writes to $8001. See code below. It looks kind of strange? I can't find any document behaviour for this. Mapper 151 docs has vanished from NESDEV Wiki aswell (or if not, it's very well hidden)..
Code:
LDA $06F2 = #$00
STA $8000 = #$0F
LDA $06F4 = #$00
STA $8001 = #$09
LDA $06F3 = #$00
STA $8000 = #$0F
LDA $06F5 = #$00
STA $8001 = #$09
STA $8000 = #$0F
LDA $06F4 = #$00
STA $8001 = #$09
LDA $06F3 = #$00
STA $8000 = #$0F
LDA $06F5 = #$00
STA $8001 = #$09