Letterbox vs scale

Using the FCPX Letterbox plugin seems somewhat incompatible when using the scale parameter - because the borders are affected by the clip scale adjustments.

Is there a recommended 3rd party Letterbox plugin or approach that has integrated scale? (along with offset)

I prefer not to compound clip everything.

Not sure why your reluctance to use a compound clip in this instance, but another option is to use an adjustment layer.

Thanks Tom....

Just that I have so many of them for this music video -- didn't want to have a whole other set of clips to keep track of. I'll give the adjustment layer approach a go.

Adjustment layer is the way to go. Alex4D actually made an adjustment layer version. Granted it is older and might have a few issues, but it works for my purposes:

blog.alex4d.com/2011/07/22/fcpx-widescreen-matte/

The other option you have is to simply change the resolution of your timeline/project to be the aspect ration you need, that is if your delivery is different from 16x9.