The ratio of shrubs to plugs is up to the discretion of the gardener. Many gardens rely far more on plugs than shrubs, so a normal response would be between 70 and 90 percent. The ratio is ultimately up to you, though!
As a note, the calculation is based on one plug per 2 square feet. If your planting differs significantly from this spacing, it will make the estimates of this tool inaccurate.