boundary floating above the ground

I am new to VR development, when I used the blueprint template, the character feels like floating rather than standing on the firm ground.
When I changed my physical position, the boundary I set is also moving slightly (like floating) against the floor in game.
This issue caused a dizzy feeling, anyway to fix it?
And this problem only happens in engine version 4.18.1

When I used engine version 4.17.2, there was no such issue. But the boundary is a foot higher than the floor in the game, feels like I am standing on a air wall.
I guess these problems are caused by similar setting issue. Anyone got some tips to fix these problem?

Many thanks.

On the following documentation page, you will find two How -To’s that will go over setting up a camera for a seated or standing Vive experience.

cheers, will try it out