It is generally suggested that the front of the loudspeaker be placed 3ft (approx 90cm) from the front wall as a starting point.
The midrange is approx between 3khz and 90-100hz
The wavelength of a 200hz frequency is approx 171.6 cm. The half wave would be 85.8cm (approx 34.2 inches).
The wave is spherical in nature, so half the wave wraps around behind the loudspeaker and the other half wave is in front of the loudspeaker.
The lower frequencies of the midrange lie between 400hz and 90-100hz.
As the loudspeaker is moved nearer to the front wall (2ft) the lower end frequencies get reflected off the front wall - as a result these lower frequencies reinforce the lower frequencies of the front half of the soundwave and we begin to hear muddiness in the midrange.
a simple test would be to - with your back to the front wall start speaking with a consistent loudness - now slowly walk away from the front wall until your voice sounds more natural (ie: without the reinforcement of the lower midrange frequencies). This too would be a good starting point for the placement of the loudspeaker.
I hope this helps.