If you concentrate on the ‘fists’ you will miss all thats going on behind them. There is a reason for the odd elbows in strikes.
The striking is two fold, iow the elbows and the wrists are held in certain alignment to allow a conceptual attacking idea to work.
Without the attacking idea we could just flail away with the same stuff everyone else does…
To be able to attack with abandon and spend little time thinking about your own defense the elbows are held inwards …like old time bare knuckle boxers. But the similarities end there.
The reasons for the arms being held in is to make the forearms hold acute angles PRIOR
to becoming a full strike whereby the elbows leave their positions to strike, recovering back for the next cycle etc…
The force we can generate is quite surprising, considering we cant chamber or recoil back like a big haymaker :D…reason, we are using our forearms as an alternating line of deflection force, ballistic force, generated by short controlled focused strikes to the target areas and back again. The force being generated in several ways. Primarily from structured delivery from the ground [ etc…] hips [ hips big part] to the movement of each fighter.
Like any fight some punching timing gives more power than others …we can use timing as well to gain force too.
With a combination of several actions …we can develop some decent stopping power 
I can attest to that from an ill spent youth …ok ill spent mid life…I have hit quite anumber of guys in my past [ I can hear terence warming up his fingers now :D] bar trash they may have been but they could take a punch
like any good fighter…but the point being punch power of the vertical punch…
Its vertical because thats the position the fist takes when you squeeze your elbows inward. Its actually more like a upper cut combined with a cross…elbows low forearms curving in, trying to maintain the inward angles so they ‘cut’ any entry lines , one at a time as they swap out along a flanked arm/position etc…
Only a line of defense , not the be all end all of the striking system.
A basic training exercise in WSL VT is to face a heavy bag in a stance you choose, lead leg for a drill…then keeping your fists so they are like 2 uppercuts , keep your elbows in front of your stomach and alternate blows to the bag while keeping the arms the same positions back and forth 1-2-1-2-1-2 hitting with the elbows in in front of your stomach etc…you can generate force , but the key factor is to develop endurance for striking with elbows inwards …not to deliver body shots from a clinch face on…the strikes go in directly to the bags center not like an upper cut …just a drill for elbows while the strikes are in a tan /elbow position moving in and out repeatedly…
The record stands at 40 minutes Desmond Spencer ! 5 minutes and I am crying … the endurance for keeping the techniques working along with some stamina in general for fighting …and not collapsing under attacking pressure from a similar partners attempts to make your elbows go out and allow entry easily.
drill not a reality. [Sorry T]
In chi-sao we practice 'when the hand is free strike the partner with sufficient force from heckling to hurt them ’
not just tag, but move me you big girls blouse, you call that a punch etc… the inch punch can prove the force or no force easily…
You can also show how to ‘rob’ the opponent of space to generate force by attacking them…an inch forwards will take quite a bit of force from a strike …we don’t block by allowing strikes to hit us in the head , just to show the bad timing on the partners part…ergo to slow, or the elbows came out as the punch landed allowing a counter punch to land as they hit you…they try to close the elbows down and forget to strike you with force etc…you can see the simple idea of the drills …not sticking …STRIKING and simultaneous deflecting in smooth single actions that don’t involve wrist actions , but inwardly held elbows…which lead to a
vertical fist.
many concentrate on the ‘fist’ missing all that heavenly gory, er glory I meant, not gory…
I love that movie !