I think it might be more that the Rebo statue is oversized for 1/7 than that the bust is undersized for 1/6. But with these characters it's really hard to tell sometimes, because we didn't see anything on screen that allows us to easily compare sizes.
I had the GG band statues (which is one of the best sculpted SW collectibles ever) but it just didn't work with my 1/6 palace set-up - they were all about 20-30% too small. You can see in some making of pics and also a few palace pics that Max is bigger (and Sy and Droopy should come up to armpit level on people, but the GG ones were more like waist level to 1/6 figs.)
I was really hoping that the new Max mini-bust would be that 20% larger to make it work, but if it's the same size, then I guess it's back to waiting for SSC...
A Jabba's Palace set-up really needs the bright colors that Sy and Max bring...