The 146/RJ landing distance credit for steep approaches is in two parts.
First the distanced gained from the geometry of a steep approach and the allowable use of the 35ft threshold crossing height, and:
Second, the use of actual steep approaches (flight tests) to determine the AFM landing distance, thus gaining credit for the demonstrated flare performance vs simulated / calculated alternatives.
The 146/RJ, like other ‘STOL’ aircraft have high lift characteristics and usually very responsive pitch control systems; the positive benefits enable a sharper / later flare at a lower altitude (but be careful to avoid the tail scrape if the flare is too late).