You may be ok being it's in a box and you have a backflow preventer , I would check with the city to see if they have a code in place. In cold climates hose bibbs/frost proof hydrants should be above snow levels.
Thank you. This is Texas so not much snow. I did look in the plumbing code and did not find anything. The city did want the vacuum breaker installed but did not say it was a problem as far as the height,