I’ve never used that program, but I’d try tweaking the inputs of VE and peak rpm until the predicted flow requirements get closer to the actual head flow.
The current read out is only looking for a head flow capacity that’s 50cfm lower than what’s available.

Based on the old superflow formulas, a 499 with heads that flow in the 440 range should be able to peak in the 8400-8800 range.

Using the 387cfm number the program spit out puts the estimated peak at 7400-7800.