Airflow in this region is predominantly turbulent so there's not much point in concentrating on shape. The things that matter are:1. Ensure the pellet's skirt is seated past the barrel port2. Ensure the probe does not represent a restriction. By that I mean I restriction relative to everything upstream that precedes it. Referring to the graphic below:valve inletbetween the poppet and valve bodythroat minus valve stemexhaust minus valve stemtransfer portbarrel portI plug my numbers into this little spreadsheet to help me see where potential restrictions are:A copy of the spreadsheet is attached.