They will stay in place just fine. I've never had a problem. If you want to make them tighter, you can line the inside of the mount with a small piece of gaffers tape but it isn't really necessary unless you use some other caps like the dpa4023s.
When you run them in the field, you shouldn't let the cable hang like you have them in the picture. Loop the pair through the strain relief of the A20S so that if you take a beach ball hit the capsule can't fall to the ground.