Oil can bypass the rings or valve guides and produce noticeable smoke. (Noticed when off the gas—
coasting in gear—then accelerating).
Oil can leak past the rubbery flywheel seal, and leave noticeable stains under the parked car.
Oil can leak past the valve cover gasket, leaving the engine (and engine compartment) coated with oil.
Oil is leaving your Scion somewhere, so physical evidence should be apparent.
Is the dipstick the same one that came with the car? (IOW, is it the original or a replacement?) Check the tip for condition. If the dipstick is damaged—
or too short—you could be overfilling the sump.
Before oil changes, did you try the Shell Rotella 10W-40 procedure?