WIX: Windows Installer patch generation. Patching al previous versions?

I have a WIX patch that I need to apply to all client PC's with a particular product installed. I generated the original MSI and have the WIX script that was used to create it. The process has gone like this:

MSI installer v1.0 created and distributed to 50% (ish) of client machines.
MSI installer v1.1 created and distributed to other 50% of machines at a later date.
MSP patcher v1.1 created to patch all original 1.0 installations to 1.1.
MSP patcher v1.2 created with intention of patching all version to v1.2

The issue is this: The 1.2 MSP will install fine on clients with the 1.0 MSI, and clients who have 1.1 installed, as long as they were installed with the 1.0 MSI and then PATCHED to 1.1 using the MSP. Clients installed using the 1.1 MSI will not patch using the 1.2 patcher. IS there a way of correcting this in my patch file? Or is this behaviour by design?

1.2 Patch.wxs is attached as a code snippet.

Help is much appreciated!

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
    <Patch
        AllowRemoval="yes"
        Manufacturer="Company"
        MoreInfoURL="http://www.site.com/"
        DisplayName="EDScripts 1.0 to 1.2 Patch"
        Description="Update to all Scripts files."
        Classification="Rollup"
        TargetProductName="ED Scripts Package"
        >
       
        <Media Id="5000" Cabinet="RTM.cab">
            <PatchBaseline Id="RTM"/>
        </Media>

        <PatchFamilyRef Id="EDScriptsPatchFamily"/>
    </Patch>

    <Fragment>   
        <PatchFamily Id='EDScriptsPatchFamily' Version='1.2' Supersede='yes'>
            <ComponentRef Id="component0"/>
        </PatchFamily>
    </Fragment>
</Wix>

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