popover, smaller size?

I'm showing a popover with a short list of items to choose from. I'd like it to be pretty small, but I can't seem to control the size. It's too big, with a lot of extra space around its content. Anyone know how to control the popover size?

    VStack {
        Button(action: { self.showPickerPopup = true }) {
            Text(pickerTypeButtonText)
        }.popover(isPresented: $showPickerPopup) {
            List(self.choosablePickerTypes) { ptype in
                Text(ptype.displayName).onTapGesture {
                    print("picked \(ptype)")
                    self.showPickerPopup = false
                }
            }.frame(minWidth: 0.0, minHeight: 0.0)
             .frame(width: 200, height:300)
             // ^^^-- these frame calls are ineffective
        }
        Spacer()
    }