There are several places in your system where can disable auto-scaling options. Disabling it in your graphics driver is the most obvious.. and in some strange cases, there is an option in the BIOS that causes it. If you continue to have problems, perhaps you can look there.
Once all the system scaling stuff is disabled, it's pretty easy to get dosbox to scale the image and to understand what is happening.

The monitor itself can also control scaling and can be configured in the OSD.

ADDiCT wrote:

Stop ... nonsense ... for god's sake ... crying ... severe case of PEBKAC ... shut the f**k up ... that you'll never understand ... Geez.

Whew, ADDiCT, I don't care for fancying what it might be like to ever be somewhere near you the day you should get a little little bit edgy 😳
To assuage the discomfort, may I suggest to take advantage of a couple of tiny cooking treats promoted ad hoc by good old Mark Twain (A Tramp Abroad) :

RECIPE FOR NEW ENGLISH PIE
To make this excellent breakfast dish, proceed as follows: Take a sufficiency of water and a sufficiency of flour, and construct a bullet-proof dough. Work this into the form of a disk, with the edges turned up some three-fourths of an inch. Toughen and kiln-dry in a couple days in a mild but unvarying temperature. Construct a cover for this redoubt in the same way and of the same material. Fill with stewed dried apples; aggravate with cloves, lemon-peel, and slabs of citron; add two portions of New Orleans sugars, then solder on the lid and set in a safe place till it petrifies. Serve cold at breakfast and invite your enemy.

missing the cloves, or as a stirrup cup

RECIPE FOR GERMAN COFFEE
Take a barrel of water and bring it to a boil; rub a chicory berry against a coffee berry, then convey the former into the water. Continue the boiling and evaporation until the intensity of the flavor and aroma of the coffee and chicory has been diminished to a proper degree; then set aside to cool. Now unharness the remains of a once cow from the plow, insert them in a hydraulic press, and when you shall have acquired a teaspoon of that pale-blue juice which a German superstition regards as milk, modify the malignity of its strength in a bucket of tepid water and ring up the breakfast. Mix the beverage in a cold cup, partake with moderation, and keep a wet rag around your head to guard against over-excitement.

...won't apply ? C'est dommage.

---------------------------------

ripa wrote:

...
If you set aspect=true, fullresolution=1680x1050 (or whatever your display's native resolution is), fullscreen=true and output=ddraw then every game (except text mode) should be zoomed correctly (pillarboxed - black bars on the sides) and your driver settings shouldn't have any effect because those (the driver's) settings only affect non-native resolutions.
...

thank you very much for taking the time to share all this interesting detailed info.
If my reply doesn't come exactly @warp speed, it's neither because of sloth nor of PICNIC, but just because I was testing those settings.
Personally I don't have problems with pillarboxing & stuff, or should I say I stopped having after finding a way with the global driver settings, which of course doesn't impinge on the output & fullres options in dosbox.conf you pinpointed.

A question if petty seems to linger though 😕

I understand output=ddraw is *the* way to go it in a sense, at least as regards the stretching issues (if I got you right), but :
what if you want or need to have direct3d ?
Wouldn't this mess up the scaling thing ?

direct3d handles stretching a bit differently from the other outputs...mostly depends on what I like most 😉