The elevation data displayed in Garmin Connect is, in my humble opinion, not currently displayed in the most useful way.
Let me first describe what currently happens. Elevation data is presented with the positive elevation range far too large for the given data. To compound matters the same excessive elevation range is presented for both positive and negative elevations concurrently, even though most people will never ever experience negative elevations (below sea level), and even if there are no negative elevations recorded in the data. The net result of all of this is the vertical squashing of the presented elevation data. One has to manually zoom to re-scale the elevation range to only display the data, and not the empty space too.
Let me now suggest what I believe to be a rational solution. Prior to displaying/presenting the elevation data, the maximum and minimum elevations recorded in the data should be obtained (by searching through the data if necessary). The elevation range presented should be from the minimum elevation recorded to the maximum elevation recorded, no more, no less. Simple :).