Circuit height is also dependent on airfield elevation...I did my initial training on an airfield 5000ft above sea level in a cessna 150, and many a time we rarely got to circuit height given the hot and high conditions.
If I were to try and make my circuits smaller I would just ensure, as other posters have eluded, that all your turns are not too tight and that you're well away from the stall. Which incidentally doesn't mean that you must fly the whole thing at 50'!
What I can say is . . . practice and the more comfortable you feel the better you'll become and of course never be overconfident. I was once, luckily it was on my BMX when I was a kid.
