[Mandobart]

IMO the hearing issues you describe likely means that we don't hear the same things. My observations on arm rests and sound ports probably won't align with yours.

I've been using chinrests on my fiddles and armrests on all my mandolin family instruments (8, mounted with viola chinrest hardware) and John Pearse stick-on armrests on 4 of my guitars.

I only have sound ports on one instrument, an F5 mandolin.

The whole idea of sound ports as I understand, is to help the player hear their instrument, like a monitor. TBH I don't hear any difference between my sound port mandolin and all the others.

The whole idea of arm rests as I understand, is to prevent the picking arm from damping the soundboard to improve tone and volume. I believe the combination of the armrest and Tone-gard on several instruments has resulted in higher volume and longer sustain. One other function of an arm rest is comfort. I recently added a clamp on arm rest to my T1K tenor ukulele due to discomfort from the small kind of sharp edge.

But ultimately aesthetics are always part of the picture. I've decided for now no arm rest on the HD-28 or 000-15SM.