I went with creating JavaScript functions that allow for me to specify % sizes, physical sizes, etc...:

Qt Code: 
  1. //returns a density ratio of the current screen
  2. function appDensityRatio () {
  3.     return appWin.appDensity / 11.6129;          //appWin references the main window, and appDensity is set to Screen.pixelDensity
  4. }
  5.  
  6. // returns the pixels that equate to the provided inches
  7. function inchHeight(myInches){
  8.     if( appDensityRatio() < 1.0 ) {
  9.         if( appDensityRatio() >= 0.70 ) {
  10.             return Math.round(myInches*(appWin.appDensity*25.4*appDensityRatio()));
  11.         } else {
  12.             return Math.round(myInches*(appWin.appDensity*25.4*0.70));
  13.         }
  14.     } else {
  15.         return Math.round(myInches*(appWin.appDensity*25.4));
  16.     }
  17. }
  18.  
  19. //returns a size as a percentage of the given size
  20. function psize(pcent,fullval){
  21.     return pcent*(fullval/100)
  22. } 
  23.  
  24. // returns the pixels that equate to the provided point size
  25. function pointHeight(myPoints){
  26.     if( appDensityRatio() < 1.0 ) {
  27.         if( appDensityRatio() >= 0.70 ) {
  28.             return Math.round(myPoints*Math.round(appDensityRatio()*(appWin.appDensity*25.4)/72.0));
  29.         } else {
  30.             return Math.round(myPoints*Math.round(0.70*(appWin.appDensity*25.4)/72.0));
  31.         }
  32.     } else {
  33.         return Math.round(myPoints*Math.round((appWin.appDensity*25.4)/72.0));
  34.     }
  35. }
  36.  
  37. // returns the pixels that equate to the provided point size, used for FONTS only
  38. function fontHeight(myPoints){
  39.     if( Math.round(appWin.appPixelRatio*fHeight()) < 1280 ) {
  40.          return Math.round(myPoints * 0.75);
  41.      } else {
  42.          return myPoints;
  43.      }
  44. }
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Then I can set a size on the base window... and size everything on that size...
Qt Code: 
  1. ApplicationWindow {
  2.     id: main_window
  3.     objectName: "main_window"
  4.     x:0
  5.     y:0
  6.     width: Screen.width
  7.     height: Screen.height
  8. }
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Child windows are sized with
Qt Code: 
  1. anchors.fill: parent
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and all child window objects are sized to their parent with calls like so:
Qt Code: 
  1. Rectangle {         //Child Window (included in Main using a StackView)
  2.     id: graphWindow
  3.     border.color: "red"
  4.     border.width: 2
  5.     radius: 10
  6.  
  7.     Rectangle {              //Child object
  8.         id: wspdChartRect
  9.         color: appWin.rectBackColor
  10.         anchors.left: parent.left
  11.         anchors.leftMargin: Funcs.psize(1,graphWindow.width)
  12.         anchors.right: parent.right
  13.         anchors.rightMargin: Funcs.psize(1,graphWindow.width)
  14.         anchors.top: parent.top
  15.         anchors.topMargin: Funcs.psize(1,graphWindow.height)
  16.         height: Funcs.psize(48,graphWindow.height)
  17.         width: Funcs.psize(98,graphWindow.width)
  18.         border.color: "red"
  19.         border.width: 2
  20.         radius: 10
  21.         visible: true
  22.     }
  23. }
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