I think the DPx HEST is probably my biggest small knife, though I have a few other knives that do a great job. There are a couple of key points to making this happen.
The first is reducing 'unuseable' overall length. If it's not cutting edge, and it's not handle length, get rid of it. Ricasso, excess indexing, space taken up by manufacturing limitations, etc. all add to overall length, overall weight and reduced tip control. The Rising Wolf is an excellent example above (actually all of the Bark River examples posted are great)-no ricasso or wasted space between useable handle and cutting edge, and the minimal space not used for grip or cutting edge is the rounded pommel of the grip. The RAT-1 is a very poor example. It has a HUGE ricasso, large sloppy manufacturing space of the handle before the ricasso, and leaves you with more than an inch of wasted space between the grip and useable edge.
The second key to getting the most use out of a small knife lies in the blade profile. Having a working point and the longest amount of usable blade length is important. The more curviture you can pack in the same blade length, the more slicing edge you have-IE, belly. There's a line between creating the most functional edge in the same amount of space and overdoing it-some manufactured recurves add so much that it takes away from the practicality by making sharpening a pain in the butt, drastically increasing the complexity of use, etc. Usually the more belly you have, the less of a pronounced point you wind up with, but dropped and clipped points can help maximize both usable edge and working point, while centering the point along the axis of the handle for ergonomics and ease of use. Dropping or clipping the point to where it reduces most of the belly is inefficient, and alot of otherwise great knives-like Spyderco for example-drop the point too far and leave you with less working edge and don't really offer any benefit. I don't have any knives dropped past a spear point for this exact reason. The HEST has some fantastic belly, as do the Izula and most of the Bark River designs offered above.
If you can wiggle in ergonomics for blade control while reducing hand fatigue into these two points, you will have an effective little big knife. The HEST has some very slight unusable space-there's the tiny bit of pommel guard, tiny bit of integral guard and the wire breaker/fire striker at the base of the blade, though these are sacrifices of weight and overall length for better ergonomics and multipurpose functionality. The blade profile with a very efficient drop point and fantastic belly definitely help overcome this. The RAT1, otherwise one of my favorite user folders, also has a near perfect edge profile and drop point, but I find the unusable space between the cutting edge and the handle just horrendous. Not only does it increase weight and bulk, but it also reduces ergonomics and tip control.
These are just my personal opinions about knife design, they probably aren't perfect. Of course there are particular specialized designs for particular purposes, like wharncliffes, hook knives, etc- sure they have their purposes, but when talking about the most efficient small allarounder, I apply these scrutinies when purchasing my knives. *hint hint, all you knifemakers