I have a different perspective. Going back to my old career as an engineer and quality control manager, we used a term called "stacked tolerances". This means that if you have for instance three parts and each is near the outside acceptance criteria of their measurement (although still within the acceptable specified tolerance), the combined effect when the parts are assembled together is that all the "tolerances" are added together to produce a less than optimum part.
So while as Ken states the maximum distance between frets on a 28" and 25" scale may only be 0.2", when you play a chord you have to add ALL those "tolerances" together. So if you play a Bm chord on the 5th, 3rd and 2nd fret in DAD tuning, the difference in distance is 1/2". That is a pretty big difference in stretch for someone with small hands.
If I play a 28" dulcimer for ten minutes or so, then switch to a say 25" or 26" I notice a big difference in ease of playing. In fact, doing this is a great way to warm up. In my old band days I would play a bass for 15 minutes or so before grabbing my Les Paul and heading out to the gig.
updated by @ron-gibson: 03/16/19 01:22:28PM