A semivariogram, covariance, or cross-covariance cloud depicts all possible pairs of points for a range of lag distances. The default dataset of 300 points totals nearly 45,000 point pairs, and even these can be difficult to display and interpret.
Datasets with hundreds or thousands of samples should be restricted to smaller domains, to avoid overcrowding the variogram/covariance cloud diagram.
Geostatistical Analyst default values can be changed using the ArcMap Advanced Settings Utility.
For ArcGIS, versions up to ArcGIS 8.1 run AdvAMSet.exe located in the ArcObjects Developer Kit\Utilities\VBAdvancedSettingsUtility.
For versions 8.1.2 and above, run AdvancedArcMapSettings.exe located in %ARCHOME%\Utilities.