The DA 20 Katana is a powered aircraft, but the rate of descent vs airspeed graph from
gliders still applies. Generally, the lowest rate of descent (vertically) is slightly lower than Vbg. This makes sense as higher AOA will generate more lift at the expense of increased drag, which slows forward motion. Vertical component grows larger, allowing lower speed, horizontal vector grows smaller, therefor less distance covered.
The relationship holds all the way down to near the stall point, any slower, Coefficient of Lift begins to decline and sink rate increases. A little more dangerous to fly here, as a gust of wind or a turn could lead to a stall.
If you are high over the airport and approaching to land (getting near the ground), "going slow" or being on "the back side of the power curve" is not as safe. Better to hold speed and drop flaps.
But if you are higher and wish to try minimum rate of descent (flaps up or down), "real" numbers for your particular plane can be had. Keep that carb heat on too, if needed.