Here are the Flex Radio settings for the Heil PR-781 mic.
W2IHY EQ Plus for external audio compression only (no EQ) in front of the Flex Radio.

Mic Gain:  25
DX (ON)   5

Transmit Filter:
High:  3100  Hz
Low:     50   Hz

Leveler ON

12 Band EQ:

Gain:  -6

32 Hz:     -12
63 Hz:     -9
125 Hz:   -6
250 Hz:   -3
500 Hz:  +3
1K Hz:   +9
2K Hz:   +12
4K Hz:   +9
8K Hz:    -6
12K Hz:  -12

Give these settings a try!

73'
Steve
W4YHD