Small base? No. Raid spawns cover a large area. That entire red circle you see on the mini-map basically. They are intended to spawn out of view and rush towards the player/base. If you don't have that entire possible spawn area blocked off then they are still going to spawn, though you will prevent regular mobs from spawning inside your base which is always good. No one wants to wake up to a greyling at their bedside.

As others mentioned though, them still spawning for raids isn't necessarily a problem if they are incapable of reaching you anyway. Trenches and earth walls are great for this, you can just wait out the raid timer in blissful peace in most cases (be aware of the limitations of your base defenses, like fliers are a weakness for most bases even with the trenches or walls since you know, fliers, can go right over them...or trolls can be a problem to because of their extensive reach. The trench may stop them but they can still strike things near your walls/trenches if there are things there to strike).