if your at FR99, then it's feeding Maximum amount. how is the flames on the stove?, is there about 1" ash at the end of the grate? if not, then the MAX setting needs to be adjusted. the feed rate will adjust automatically, you can adjust it thru the coaltrol it's based on the min max and room setpoints.
post a pic of your stove running at FR99.
Maybe the MAX needs to be raised a little depending on how much flames you have on the stove. Only change it about 2 points at time.
It takes a lot of time for coal to respond, an hour or more depending on how much you change the temperature settings. I wouldnt; run more than 1 or 2 degrees difference, it takes too long to get up to heat, then it will overshoot and take a while to cool back down, most of us just leave it at a set temperature.
it's quite possible the stove is not big enough to heat/maintain the temperature or raise it. depending on the heat loss in the house or it just needs some adjustments in the settings. 78 IS pretty high temp setting, like I said above, the stove may not be big enough to produce that much temperature rise.