Replacing wooden back door with UPVC question

[Gav74]

Hello.

Just a quickie...

I'm replacing my wooden back door with a UPVC one, but the wooden frame is 12cm deep, whereas the new UPVC frame is only 6cm.

The question is, would I be right in thinking that I should fit the frame flush with the outside wall and plaster the extra 6cm gap inside?

For a moment I had considered putting the door frame inset by 6cm as the sill will be plenty long enough, but that doesn't seem right.

 

[Mw Roofline]

Yes, not flush with the outer brickwork though, bring it in about 35mm if u can then plaster the inside.