Can you explain why my contact lens dioptry is higher than my glasses dioptry?

Vertex distance: The prescription strength is dependent upon the distance between the anterior corneal surface and the corrective lens. For contact lenses, this is essentially zero and an adjustment factor needs to be incorporated. This rx is less negative or more positive than the glasses rx but the overall effect is the same.

Contacts: You are far-sighted. The contact lens sits on the eye; glasses sit on the nose. The distance from the contact lens to the center of the eye is closer than the distance from the glasses lens to the center of the eye. Thus, for a far-sighted person, the lens power must be greater for the contact lens to achieve the same effective correction as the glasses.