best trick i found is to carefully use the shift function. say a road about 2 hoe circles wide. you want to place yourself at bottom of the hill, max range of where your hoe will reach, your hoe must reach top of the hill from where you are standing. do one click on each side of the road, moving to left or right for second click. now keep your position and move hoe about one circle down from where you just hoed, where its uneven really.. then do again on left/right side. keep doing this for entire slope. you can move further down after initial two hoe picks, but thats likely to make your slope steeper than wanted. also, above method is likely to make your slope longer than originally intended, albeit much nicer and 500% better for a cart.

TLDR: shift-hoe click carefully.

tho, even with this. you may have some spots that are just a nightmare due to rugged terrain that needs to be mined in a fashion thats near impossible to tell. i actually advice to raise terrain to compensate for rugged terrain instead of mining as it usually just makes it worse.