The market is not typically range bound, or flat, this much of the time. A way I've found to test this is to determine peak and trough dates combined with periods of time when the movement up and down is within a range of three percent either way. In other words, when the movement is very minor this reflects a range-bound, or flat, market that is pretty much going nowhere.
The actual percentage of time in a flat market all depends on what you require the bull and bear trending market moves to be. The following table shows a move anywhere from 7% to 20%. The date range for this on the S&P 500 is 1970 to present.
So for 20% trend-moves in the S&P 500 the amount of time in a range-bound market is 24.91%. When you drop this to 7% the time in a flat market moves down to 18.97%. If you average all four you end up with 22.40%.
This is the same thing but for the periods from 2000 to present:
The average of all four is 22.15%. So it is pretty clear that the last eleven years have not been all that much different than the longer period of 1970-2011.