Agreed ALWAYS check your putter scale ... But there is a good reason your Putter Caddy defaults to the scale it does, with the exception of the Fringe selection. Who the hell knows why it does that.
I think most would agree it is easier to hit the ding mark when your slider has less than more travel distance. So this is why your Putter Caddy is suggesting the scale it does for your putt. The higher scale will usually have the distance you need at a much less slider travel so it usually defaults to the next higher scale.
Below is my putter scale I made for my Max putter.. lets say you had a putt within 10 feet. Notice the marks for the 10 scale then notice on the 20 scale the same marks for the distances of 10, 8, 6, 4 & 2 are approximately 1/2 the travel distance then on the 10 scale. Because of that then the putter caddy often defaults in this situation to the 20 scale offering the opportunity to use a lessor slide travel length for an easier mark hit.
Notice also that the some of the same distance marks can be found at higher scales also. Those can be used and will work fine but there can be a price for miss hits.
I'm not one of the betters putters but my distances are usually pretty darn close. I find using the higher scales often help me, even for short putts. I always use my 20 scale even for putts within 5 to 2 feet.
But still You need to, as mentioned, make it a routine to check what scale it's on and select what you want to use before each putt.