Originally Posted by locallawncare.ca
Blade probably has a different offset, which means the tip is lower from center than the other blade. Most 21" mowers mulch ok but any thick wet stuff and no chance, just put the original blade back on. Here is a pic of a couple Toro blades for my 21" not sure if they are the same or not.
I had to take a 2nd look just to make sure, but I think the quoted above is the best reason for the different cut.
Here's a pic of the medium lift blade that's currently on there:
And here's the original (in desperate need of sharpening):
With the center being at a different height, that may have been the reason why it wasn't scalping like the other one is here and there.