It sounds like it's simply too bright for the LDR and you are off it's 'linear' brightness/resistance curve.
Your options are:
1. reduce the series resistors but this will increase current consumption and heating in the LDR which will make the reading less reliable.
2. shade the LDRs to prevent as much light falling on them. A trick I've used with outdoor webcams is to place a 'reactolite' photochromic lens from sunglasses over the camera lens to increase the range of light it can cope with.
3. possibly use a different method of detecting the light direction: place four LDRs as close together as possible in a square arrangement and cover them at a distance of a few cm away with a black shield. In the shield put one small hole directly over the center of the square. Now as the light angle changes the beam of light falling through the hole will fall unevenly on the LDRs to allow you to determine the movement needed to centralize it. The advantage of this method is you can adjust the hole size to cater for different light levels.
Brian.