The -srd switch suppresses the including the root directory of the path given. Using this switch will also change the values of identifiers being generated because of how they will be rooted. Change this switch with high caution and review on the impact to your product.
heat.exe dir C:\MyDir -sfrag
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<DirectoryRef Id="TARGETDIR">
<Directory Id="dir86787CC870C17D6ABA6D1CDCBD925324" Name="MyDir">
<Directory Id="dirAA5EBADF0D0CC654BAD8E2CEFBF96609" Name="one">
<Component Id="cmp51B22E187A7403EF3A8EB589174E89DC" ...="">
<File Id="filEA449989D4339EB8C7329B93F83D35FE" ...=""/>
</Component>
</Directory>
heat.exe dir C:\MyDir -srd -sfrag
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<DirectoryRef Id="TARGETDIR">
<Directory Id="dir090ACB8E8D9B8C1F26DE6E8300AA9049" Name="one">
<Component Id="cmpE21824A6879A478E4A884BA6B00C33C9" ...="">
<File Id="filF1BA1271365EB2A130AA3F0BE83E9D6D" ...=""/>
</Component>
</Directory>