Sparklines very narrow - but not for all time periods

Hi there, Any ideas why sparklines would be so short/narrow? I'm seeing that for shorter time windows - e.g. less than 4 days - the sparkline shows as expected. But once I extend it to a longer window the sparklines are very compressed. ![alt text][1] Is that a common issue? Thanks, Phil [1]: /storage/temp/274785-splunk-sparklines.png