Father does not mention that St Pius instituted the Scapular Medal as a substitutes for the small Scapulars basically as in indult for people in the tropics, where the cloth Scapular might be uncomfortable, not as a general replacement.
I've mentioned that I wear the Scapular Medal to replace the Four Small Scapulars of the Five that I'm invested in because the cords of a second Scapular, were I to wear a Fivefold, would get tangled with those of my Tertiary Scapular. The Scapular Medal does not substitute for the Tertiary Scapular. However, I live in the Great Plains of the United States. Temperatures of 100 F (38 C) are not uncommon during high summer, and it can be quite humid as well. I have never felt that it would be necessary to use the Medal, even if I wasn't wearing the large Scapular, and I'm sure it's much more uncomfortable than the small Scapular.
I'm not sure if Father's 'Dictionary' was written before the change, or he just made a small mistake, but any Priest with faculties now has faculties for investing in the small Scapulars.