Dear Tang,
Two different items at the start: No references to stabbing, please.
I was fine going along until the ad hominem part.
As regards pinggg or tinggg - I take that more about the articulation of the musician and the doing the striking. Among musical instruments, a raw metal on metal sound, to my ear, invariably evinces a hardness in the initial attack. Maybe a leather wrapped striker might give something like a ping versus a ting. I find it very difficult - to the point of avoidance - to replicate the actual sound of instruments verbally or with words. But there may be people who do something like that. I think your question is best answered in practice rather than here. Maybe Ack's video is enough.
Your example of test conditions, as told to Ack, are different than what I talked about for an example explanation of resolution. (Viz. "The system had such resolution I could hear that the percussionist was striking the triangle on its interior, each side in turn.")
Our examples (and our purposes in giving them seem quite different.
I imagine the Triangle before it is bent, as a straight metal rod. With that there is no inside or outside and likely no difference in sound when struck anywhere in the same portion of its circumference. That's only speculation on my part, but I would not bet agaisnt it. (Perhaps the way the rod is held could make a difference?)
The actual instrument is of course a different shape. Why do you think that is? Maybe the triangle is more compact for portability - though that's not a concern for other percussion instruments. I think one reason is that the triangular shape allows use of different techniques in playing it. Why would there be a need different techniques? Could that be possibly to create different sonic effects, i.e. ways of playing a Triangle that sound different? I can imagine the light single touch of the Triangle for accent as used, say, by Tchaikovsky in his 4th Symphony and elsewhere. I can also imagine the rapid striking of the Triangle interior to express Alarm! as in a Shostakovich piece. There may be ways to play the Triangle that lead to different sonics other than differences of tone and timbre, as well as those differences.
From my response to Peter A that you quoted: "...There is a technique where the instrument is struck on its interior sides in rapid succession. Side one, two, three then repeat and do it quickly. The sound can be different than striking the outside quickly and successively in the same spot. In the former approach - the dinner bell strike as it were - the interior side struck has time to resonate longer before being struck again. The motion of the musician in making the strike, possibly circular on the interior, whether glancing or direct can be a factor. ..."
Kind regards,
Tim