The hardware bridge across the top was known to be a mistake 70 years ago. 2 small coil springs can hold the plate down from underneath.
The radius shown has reached the point of vanishing returns (very little gain above 3/8": Vizard), but IDK if the filter itself is too close to the entry; another inch added front and rear might help.
The lowest pumping loss/highest CFM for a given entry has a 3/8" (or more) submerged floor, and the bell has a 3/4 (270°) rollover radius.
All of this may be insignificant on anything but a maximum effort engine.
Keep in mind that air movement in that can is not continuous, it occurs in bursts.