Scopes on break barrels are often frustrating when it comes to accuracy. The barrel doesn't always land back in the same exact position when it is closed. Just a very slight difference makes a big difference 25 yards down range. With sights they are fine because the sights are on the barrel.
An underlever springer solves this problem. The Diana 460 is the one I have my eyes on.
That has not been my experience. I have owned several break barrels and 1 underlever (RWS M46). Accuracy has more to do with overall quality and power level of rifle than how it is cocked or where the scope is placed on the action. My most accurate spring rifles have been break barrels with scopes mounted on the action - 2) R7's and a FWB 124 to be exact. Closely followed by an R9. The RWS rifles have been good, but not up to the Beeman R series rifles that I have owned. Triggers were not as good and the overall cocking and shooting/spring action was not as smooth, which I believe made them slightly more difficult to shoot well.
Scopes must be mounted solidly with quality mounts. I think this is where many of the package deals go wrong. They put on cheapo .22 lr mounts and they slip and slide on the rail. Scopes need to be of decent quality with etched reticles. I like Nikon Prostaff EFR 3-9's.
I'm considering selling my R-9, PM me if interested. My hunting spots are being developed and the R7 is all I really need for target and smaller game.
