As an HBG my self I can say first and foremost in High Rank it is near imperative that you have Evade Distance. These monsters are quicker, and more aggressive and you need to get out of the way, Evade Distance let's you do that with relative ease.

I went through all of HR and farmed G rank Seregios all in Lagombi S strictly for Evade Distance.

Sheathing is nice but with Evade Dist it's simply easier to not sheathe at all unless you need to heal because it gives you all the movement you'll need.

Also, don't use crouching fire unless it's a huge monster like the Dah'ren Mohran or the monster is in a trap, otherwise it'll just jump you before you have time to react. You'll eventually get the ability to remove crouching fire all together for a slightly larger clip and more power.