"BIG" planes are NOT more stable by virtue of size.
Though the comments about scale effect, or "Reynold's Number" are true, any RC plane flying more than say....15 miles per hour with a 12 inch cord wing is not flying in the dreaded "Low Reynolds's" number region. By this I mean, all the really nasty persistent laminar flow and separation bubble effects mostly happen with slower planes that don't have intentional or inadvertent turbulation.... (The effects can happen up to 500,000'ish Rn... but are much less likely especially with the manner our wings are fabricated.)
What you are more than likely experiencing with a large model is improved DAMPING!
If a plane has high enough damping, you can easily fly an unstable airplane.
Damping: Tendency for a disturbance, in pitch, yaw and roll, to be quickly stopped. Aerodynamic forces easily and substantially overcome inertia.... with low tendency to oscillate.
Add to the improved damping the fact you can see a large plane better.....

IMHO