[Dewy]

I have a lot of trouble "Improvising" over a major key... but no trouble with the minor keys and minor pentatonics. And I see where your coming from by using the Amin over the Cmaj... but its not the real answer. To start with Amin pentatonic has the root of A and is built around (and flows most smoothly) the root of A. Forcing a C on it (which is in the scale) doesn't cut it in my opinion.

That having been said, it is most important to refer your "soloing" to the rhythm, and play notes that correspond to the chords being played underneath your solo.

I find myself writing a melody line to play variations of when soloing over a major... just a way I try to overcome a default limitation I haven't defeated yet.