While there might be a bit of difference in the toggle pressure (and thus the force required to flare it) between a larger and smaller canopy, the difference is fairly minimal. In my experience, different canopy types can vary more in the required toggle pressure than a step down in size will generate. In general, I would recommend against downsizing. It's overrated, especially to 'solve' landing issues. The effect of small errors in asymmetry is magnified when you are under smaller canopies, and doing it right is a matter of technique much more than force.
If it's an issue that pops up only after ~5 jumps that day, and combined with general body fatigue, it might be your body saying that it's been enough for today. Listen to it, you won't get hurt by not doing the final jump of the day. (Or plan ahead if someone is organizing an awesome sunset jump, and take a breather in the middle of the day).