With the LX200 at that focal length the image scale is around 1"/px, so you need to adjust that in the plate solver. With this camera, you may see severe vignetting with the LX200, so although reducing the "Frame size" setting is typically only necessary for wide fields, in this case you may need that so the star detector ignores the distortions in the corners. There's the added chance that the vignetting is so severe that it affects the background so much that adjusting its sensitivity may be needed, or the Flatten Background adjustment should be applied, or the image should be cropped.
The short tube refractor probably has an image scale close to 3"/px with your camera. For both instruments, you may want to do a blind plate solve to get the correct value if you want to avoid having to calculate it yourself.
With the LX200 there may not be enough Tycho-2 stars in the field of view, so for that the UCAC4 or USNO-A2.0 catalogs probably should be used.