Red will field render any asset added to the wells in fcp or imported into red via the boris UI when using it as a generator in FCP. That was recently fixed. What was not fixed was field rendering of assets created in Red (i.e. text, splines, etc). The easy work around would be to add a slug to your timeline, apply red as a filter to that slug and you should have accurate field rendering and be able to make the comp any size you wish. This is of course just a band-aid solution that needs to get fixed. Unfortunately, I have not heard any news on when that fix will be implemented but at least you can get your work done, however inconvenient it may be.