To me, the blades are similar in terms of openness. The difference lies in where the pocket is. With the p92, the pocket is in the middle. With the p28 the pocket is more towards the toe, about 1/3 of the way down from the toe compared to 1/2 with the p92.
The p28 is for the toe shooter, and tends to be more unforgiving. If you don't shoot the puck off the toe, the puck tends to not get off the ice because there's more flat area towards the middle to heel. But if you have the puck too much towards the toe, you can scoop/hook it into the rafters.
If you get it in the sweet spot, the p28 gives the puck a little more zip.