Phase problem, help needed with measures :S

[endrek]

Hi, i've build a bass reflex box. And i'm doing some measures to the box to see the Frequency Response (FRF).
My box is a 140L with 2x 12MI100 beyma + 1 CD755Nd beyma + TD595 horn Beyma + Filter FD212 Beyma (fc=1,2KHz).

well my problem is, i finished the box, and started doing some measures. When i realised i had a loss of energy aroung 1KHz, then i thought "ow, it is the cut frequency of the filter, i can't do anything".

But then accidentally moved the microphone to another position, exactly to a diferent heigh. Well, what i saw was that this loss of energy that was around 1KHz had now moved to another frequency.

My suspicious says, maybe the problem is:
all three drivers have different lenght to reach the microphone, so there might be different path lenght to the measuring point, so there are cancelations right??? i.e: for 1KHz wavelenght is 0,343 meters, if there is a diference of path of something like 0,17m , there we cancelations right?? If so, how could i do the measures without "faking" them due to this effect??

well here it goes the graphics so you can try and help me with my little "experiment" i tryed to do to solve it, without reaching anywhere...

First of all, I did the measure at 1meter from the speaker and started from the "floor", wich I named as "0cm". And started going up 20cm by 20cm. Here are the graphs:



Finally, once i see that everytime i move the microphone the loss of energy moves frequencialy... I decided to "try" to change polarity of the 12''s. I inverted the polarity and measured again, and compared it with the "heigh=60cm" wich was the one that gave me "better" results..(with better result i mean....less losses of energy...), so here it is:


once i inverted the polarity of the 12''s, seemed to me that the FRF "reached" a balance between "losses" and "flat response". So i decide to leave it like that for today...Am i doing right? Am i doing something with sense?
Why did i do this and worked?Or why didn't it worked but i think it works...?
what is going on with all this.....???!??!?!?!?!?

I want answers about whats happening here because i'm really confused... Or atleast i'm really....like dunno how to solve this and take measures without faking them with this.

thx alot for your help.
cheerz from spain.