Radio checks at a desk can sound fine and still fail from the cockpit. You sit farther from the microphone, you turn your head through corners and the rig gives the mic a few more sounds to pick up. Test from the seat you actually race in.
Position the mic while seated
Aim the mic according to its pickup pattern and start with the distance its maker recommends. If hard consonants hit too loudly, try aiming the mic toward your mouth from slightly above or to one side. For more on placing a mic to limit breath noise, see Shure's microphone placement guide.
If you are mounting a boom to the cockpit, check the arm's sweep against the wheel, shifter and your path out of the seat. Compare the hardware and clearance with the ProSimRacing mic boom mount.
Test the whole call
Pick a push-to-talk control you can reach with your usual grip and verify it does nothing else in the sim. With the game in focus, ask a teammate to listen to two short calls as you drive practice laps. Press the button before you speak and hold it through the last word. Try once on a straight and once while the wheel is turned. Listen for clipped words, low volume and how much of the wheel or pedal noise gets through.
If the audio is clear but the button takes a stretch, move the binding. If the call sounds distant even at rest, test a different mic position before turning the gain up. Save the setup after your teammate can hear both calls cleanly.