Render Layers and scale in Photoshop

[guest83783]

I'm just starting to use render to layers for compositing in Photoshop.  It works great when you're rendering a lot of elements that you need to mask and edit...

But what about when you just need a certain section or layer of a file?

I turned off all the other things I didn't need, adjusted the part until it looked perfect using scene sets but when I render the part is a different scale?

Not sure what's going on here but when I open it in Photoshop it's a different size and now when I revert back to the original scene set even that render is now the wrong size.  I've tried all the standard resolutions but they all appear to be different now.

The only way I could think about fixing this in the future is to turn the bits I don't need into an emissive material rather than swtich it off and then use the clown pass to cut it out. 

Seems like a faff though.

Has anyone else had this issue, is there a way around it?

Cheers

Andy