Motherboard tells the CPU which multiplier to choose at startup, from then on the CPU runs on it. DX4 has 2x and 3x options, not sure about 1x. In AMD 5x86 2x has been replaced with 4x for compatibility with older motherboards - AMD needed every customer they could manage to get. So in most cases you just set jumpers for DX2-66 and get 5x86-133.
However, this board is late 486, and in some way more like modern boards - the BIOS has to recognize the CPU to work. So 2x setting on 5x86 results in 3x as well as 3x - the BIOS thinks the CPU is DX4. When JP12 is positionned 1-2, the BIOS recognizes the CPU as 5x86 and gives the desired 4x multiplier although the board is set to 3x. Fun, isn't it?
P.S. did you get the controller? 😀