This is a very interesting subject, but I am not familiar with piano tuning. The following is from the old manual of NI Akoustik Piano
9.2 Stretched Tuning
The term Stretched Tuning describes a tuning where the high and low registers of the piano are tuned higher and lower, respectively, tuning the low strings’ harmonics with the upper strings’ fundamentals. The piano is intentionally tuned out of Equal Temperament in order to be in tune with itself. While this tuning may be the best for solo work, it is commonly not used when working with other instruments.

I alo looked up for different tuning options in Aria Player. 13 different ones but I don't know which one would be stretched tuning. https://usermanuals.garritan.com/ARIAPlayer/Content/tuning.htm

Chris