problem for calculating time for image compression problem

Does anyone can help me with image compression in matlab, I have problem with calculate processing time? I used tic toc and cpu time function time when i make for example compressing

rinComps=50 and for PrinComps=1:10:50 that will achieve 10:1 compression ratio 5.2160

or PrinComps=1:1:5 that will achieve 93:1 of compression ratio time resulted= 3.7340 that is not logical offcourse how can that happen increasing the compression for an image will give more time not less time as i see

princomps=50
  for PrinComps=1:10:50
    VV=V(:,1:PrinComps);
  Y=VV'*X;
  ratio= 1024/(2*PrinComps+1);
  XX=VV*Y;
  XX1=uint8(XX+repmat(mn,1,n));
  end