Widget Candy : Percentage scaling not working as expected

I am using the ‘ultimate’ config.lua from here 

http://www.coronalabs.com/blog/2012/12/04/the-ultimate-config-lua-file/

It successfully scales items as expected.   I’m also using the Widget Candy scaling code :

[lua]

local physicalW = math.round( (display.contentWidth  - display.screenOriginX*2) / display.contentScaleX)

local physicalH = math.round( (display.contentHeight - display.screenOriginY*2) / display.contentScaleY)

_G.isTablet     = false; if physicalW >= 1024 or physicalH >= 1024 then isTablet = true end

_G.GUIScale     = _G.isTablet == true and .5 or 1.0

[/lua]

I have a list widget defined :

[lua]

_G.GUI.NewList(

        {

        x                 = “center”,               

        y                 = 40,               

        width             = “100%”,                  

        scale             = _G.GUIScale,

        height            = “83%”,                  

        parentGroup       = Screen,        

                caption = “”,

        theme             = “theme_5”,              

        name              = “LST_A”,          

        list              = ListMain,               

        allowDelete       = false,      

        scrollbar         = “always”,

        border            = {“normal”, 255,0, 0},

        onSelect          = gotoSceneListDetail,

[/lua]

and a button widget :

[lua]

_G.GUI.NewButton(

        {

        x               = “center”,                

        y               = “bottom”,                

        width           = “auto”,                   

        scale           = _G.GUIScale,

        name            = “BUT_ADD”,            

        parentGroup     = Screen,                     

        theme           = “theme_5”,               

        caption         = “Add Instrument”, 

        textAlign       = “center”,                  

        icon            = 13,                       

        

        onRelease       = gotoSceneAddGuitar,

        } )

[/lua]

I was expecting the layout to be similar (percentage wise) on the iPhone 4 and iPhone 5 (and iPads) however they aren’t.

iPhone 4

p4.jpg

iPhone5

p5.jpg

The list widget looks about right.   The button seem too small and is certainly in the wrong place, its too high.    Any idea how I can get a more consistent look for both devices?