Lightmix not denoising?

[Rhodesy]

Im using beta 1 and of recent releases denoising has worked fine for me with lightmix but in this particular scene / file its just not denoising my lightmix pass. I have 7 lightmix selections and each one has denoise ticked. Corona does denoise them at the end of rendering (I have it set on 0.4) but my lightmix layer looks as grainy as it was before denoise. If I go through my lightmix layers I can see they have denoised but the main lightmix pass which I would use as my base in photoshop is still grainy.

Has anyone got any ideas as to what I'm missing? Unfortunately I cant share the file and its massive!

[Rhodesy]

Think I might have answered my own question here. I've forgotten to add a layer for sun and sky which is where the noise must be coming from, DOH!