why the simulation result vary with the size of the geometry?

Dear MPB Users

When I simulate Band Gap in triangular PC, the result is different for different size of the geometry.
e.g. in simple following ctl file, when I set L=7 or L=1, the gap diagram is different but Epsilon.png files are similar after using mpb-data -r -x -7 -y -1 -n 64 epsilon.h5 for one with L=1;

 
I think  if we repeat one single row of the holes in geometry or
                   repeat  one block of holes (including 7 rows) the result should be same.
why the simulation result vary with the size of the geometry?

My be I don't have good understanding about meaning of size in definition of geometry or not fully understand of 
mpb-data -r -x -7 -y -1 -n 64 epsilon.h5


Please help.

Regards
Hassan
================================
(define L 1); or 7
(set! default-material (make dielectric (epsilon 12)))
(define Gamma' (vector3 0.2 0 0))
(define K' (lattice->reciprocal (vector3 0.5 0 0))) ; edge of Brillouin zone.
(set! k-points (interpolate 4 (list Gamma' K')))
(set! num-bands 9)
(set-param! resolution 32)

(set! geometry-lattice (make lattice 
             (basis1 (/ (sqrt 3) 2) 0.5)
             (basis2 (/ (sqrt 3) 2) -0.5)
             (size L 7 no-size)))
(set! geometry (list (make cylinder
               (center 0 0 0) (radius r) (height infinity)
            (material air))))
(set! geometry (geometric-objects-lattice-duplicates geometry) )
(run-te)
=======================================

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