yes of course it can drop. MHO% is the precentage of your opinions which got selected MHO. if you post more opinions but they don't get MHO it will drop.
you shared 100 opinions and 20 of them got selected MHO -> you have 20% MHO you share another 100 opinions but none of them get MHO. so you posted 200 opinions of which 20 got selected MHO -> you have 10% MHO
As you go through the lower levels your MHO percentage will drop radically - You may have 4/10 and be at 40% after answering a few questions but after a 1,000 questions there us no way you will be at 400 - I am only guessing here but I would say the average users MHO% is around 15 - 18.
... xD i'm no math guy but since it's a percentage, if you answer a few questions without getting MHO then obviously it will drop. That's a very stupid question but for a 13 year old I get it. Aren't you too young to be out here?