Ride, feel, adjust if needed, ride, feel, adjust if needed, ride...

There is no "directions" to feeling, this is a time where YOU decide.

To help this decision, I add my relatively "extreme" account. I could "feel" the added arm fatigue over a 40+ mile ride with my 42cm bars, I could feel that I wanted more narrow bars - much more narrow. I'm 6'1 and although its kinda odd I measured myself for 36cm bars, extremely narrow! But I got into my ideal comfortable position, measured, measured the bones in the back that are supposed to be measured, checked and double checked... then I ordered and I'm so happy with my deda 38cm (outside to outside) bars.

The ability to put my arms straight makes arm fatigue on long rides a total non-issue whereas before after mile 40 or so my arms were tired and it made me overall more tired. If I want wider I can hold the bars to get wider, if I want yet more narrow I can... but my bars now are lined up perfectly to allow me to comfortably go either way and I've quickly grown to love the overall feel. The aero benefits are likely measurable, but comfort exponentially increased when I got the "right size" bars.

I'd say it took me 5 rides to get used to it 100%. Now I grab the more common wider bars and they just feel wrong.