Conclusion

The painting

This is a lovely detailed painting where the subject and composition are excellent.

Major findings

It is not necessarily best to create a B&W rendition to use as a Luminosity layer on a coloured photo.

Interesting points

I've found a way to adjust the channels, for tone, and be able to view both the b&w and colour renditions at the same time.

Experiment

I never followed up on the perspective issue of the earlier painting, so I did a wee experiment with an uninteresting shot across the field.

Hover to see what I mean. 

I also took a number of telephoto shots and ran them through AutoStitch to create a panorama, but the program put them back into the above perspective!