I have impression I have diffilculties to make me understand.
In fact with this equation :
% MAC =( 100*C.(I-K) )/(MAC*W) + 100*(Ref.Sta - LEMAC)/(MAC)
C = 1000 for A320 / given by airbus nevertheless, for Airlingus C= 500 
K = 50 for A320 / given by airbus
MAC = 4,1935m for A320 / given by airbus
Ref.Sta = 18,850m for A320 / given by airbus
I = Compute by loadsheet
W = Compute by loading Cabin and Hold
So I deduct the only data which is able to explain difference between two register is LEMAC, no
==>% MAC =( 100*C.(I-K) )/(MAC*W) + 100*(Ref.Sta - LEMAC)/(MAC)
==>LEMAC = %MAC*MAC/100 + C.(I-K) )/(W) +
Ref.Sta
If I take my two A320
AirCraft 1 :
% MAC = 28,3%
IZW = 27,6
ZFW = 47930
Lemac = 19,5
AirCraft 1 :
MAC = 32
IZW = 49,6
ZFW = 54621
Lemac = 20,19
Perhaps I mix data which would not have like %MAC and other data !!
But I Don't desperate,
I will find this equation