Hello there,
as far as I can remember, below 14,000ft there's an allowance for a 36Kt omni-directionnal wind, plus a buffer area of 5NM where Obstacle Clearance reduces from 1,000ft to 0.
Allowance is also made for average instrument error and average pilot skill.
More accurate information should be available somewhere on the web, try a search like "instrument procedures design rules".
Hope this helps.
Cheers.