[Therion] Metapost point blocks problems

[Jackson]

Hi all,

i have made a new definition for point blocks with metapost.
It only does what I want when the point is nearby the
center of the scrap/drawing. The further the point is away
from the center of the scrap the more random the stones are
set.
Whats wrong with the definition of my "point blocks" ?

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def p_blocks_FUND (expr pos,theta,sc,al)=
     U:=(.45u,.35u);
     T:=identity aligned al rotated theta scaled sc shifted pos;
     pickup PenC;
     picture pic, henge;
     path stone, edge;
     stone := 
((-0.6u,-0.5u)--(-0.3u,-0.7u)--(0.3u,-0.3u)--(0.5u,0.5u)--(0u,0.7u)--(-0.2u,0.5u)--(-0.5u,0.3u)--cycle);
     edge := ((-0.5u,-0.4u)--(-0.3u,-0.55u)--(0.2u,-0.2u)--(0.3u,0.4u));
     pic := image(
       thfill stone withcolor 0.90;
       thdraw stone;
       pickup PenD;
       thdraw edge;
     );
     henge := image(
     for i=0 step 1 until 2 :
     thdraw pic
         rotated (uniformdeviate(360))
         scaled ((0.05u) randomized 0.1u)
         slanted 0.01u
         shifted ((0.01u,0.01u) randomized 0.5u);
     endfor;
     );
     thdraw henge;
enddef;
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Best regards
Christian (jackson)