Try to avoid multiples of two in your monitor’s placement, since you will excite the room modes of the room.
Monitors placement and listening position in the room it´s a very important factor that brings a better or worst frequency response. The situation of these element impact on nodes and antinodes in standing waves.
As a rule of thumb, you have to situate your sweet spot or listening position on 38% of the long wall it´s a starting point.
Apart from avoiding multiples of two, you need to know the room modes of your room for making a better position.
Here a great Room mode Calculator.
Let´s see an example of a room of 5,20 x 3 x 2,40 in meters.
Here we have main room modes:
Bass frequencies are our big problem on the studio. We have to situate the monitors and sweet spot avoiding resonances or pressure points as far as possible.