It's natural for boots to gather a bit at the ankle (if they didn't, then it might feel like you are wearing ice skates!), but in general, they should not slouch. Too much bunching is caused by one or more of these three factors.
1.) To understand why a boot is slouching, we first have to look at the fit around the foot. Yes, the foot! Surprisingly, this is usually the cause of boot slouching.
When the part between the ball of the foot and heel is fitted (fits snugly around the middle of the foot), this tends to give more structure to the rest of the boot.
What to Know: Be picky when it comes to the fit of the boot on your foot. It should feel like your foot is being hugged -- not squeezed or tight, but there shouldn't be much wiggle room around the center of your foot.
2.) If knee-high boots aren't tight enough around the calf, then yes, the boots might slouch.
As with any fashion item, please remember that you have to fit the largest part of your body first. For some, this might be the bust line, shoulders, hips or yes, calves. Once we fit the largest part, we can then make adjustments or alterations.
What to Know: Make sure knee-high boots fit snugly around your calf. If you need extended calf sizes, check out DUO (now Ted & Muffy), which sells boots by calf width.
3.) Another reason why boots tend to slouch is the height of the heel.
Once the foot is elevated, the boot shaft should stand a bit straighter as well. This is not a guarantee, but this can help boots from bunching too much.
What to Know: The higher the heel, the less slouching.
Lastly, be sure to take care of your boots. I sell an amazing leather cleaner on my site that works wonders for conditioning leather boots, handbags, jackets, skirts or even yes, your car seats!
I would also recommend using shoe trees or cut some foam pool noodles to stick inside your boots when you're not wearing them (you can re-use a water bottle for shorter boots). If boots are left to flop over for a long period of time, a crease can form in the fabric and that's never a good look. :)
Do you wear a lot of boots? What other fit issues happen when shopping for shoes? I'd love to hear how I can help!