If I understand what you seek in your comparison of UX designers and physical product designers-
Digital UX methodology is different than physical product research in that UX can deploy an iterative design process very inexpensively and intrinsically : that is, UX itself, can be programmed to provide design feedback to optimize a benefit to the user and/ or the producer while the product is being used. UX products can, in and of themselves, produce its own marketing feedback The feasibility of developing iterations for physical products, however, depends on the economics of product's intended market(often seen on the T.V show Shark Tank), Depending on the market economics of the physical product, it can be prohibitively expensive to determine which feature of the physical product is favorable for beneficial use, or comparable fitness for the intended market. Iterative design methods in physical products is cost effective only in cases where product differentiation is crucial in mass production and where users alternative use of another product would be devastating to the product brand, such as Coke vs. Pepsi or certain kinds of automobiles. An interesting case is tooth brushes do not seem crucially situated in the market but disposable razors are. For disposable razors see https://www.oxgadgets.com/2015/03/gille ... ation.html
Anyway, almost always, the decision to develop a physical product comes from the industrial designer's client's marketing department to determine the Most-Advanced-Yet-Acceptable product - it is not decided by industrial designers in the firm. So the onus for successful physical products, lay with the capability of critical decision making of product ideas by the client, not by a methodology by the industrial design firm.
I sympathize with your inquiry because it can end you in a quagmire of design folk-ways versus social facts. What you(and I) really need is a paper that examines industrial design firms from the subfield of sociology known as the sociology of occupations. This kind of study then could be an underlay to your psychological inquiry. I speculate,however, that a sociological examination of typical industrial design firms will reveal that the vast amount of industrial design research does not require an applied science, quantitative, or economic optimizing methodology applied to physical products, rather industrial designers produce product ideas through a (holistic) qualitative process. Almost exclusively, industrial designers create within a holistic framework that communicate the results as deliverables through artistic visualization and express them by force of personality to the client as a form of creative 'solution finding''. The product idea is then evaluated by the client's product development apparatus to determine suitability for brand management and mass production in order to be sold in a desired and applicable market sector.
I will stop here and brace myself for the blow-back from the forum.
I refer you to sources that seem situated with your academic inquiry:
Never Leave Well Enough Alone
by Raymond Lowey Historical foundation of American business and industrial design
by Nigel Cross Design methods differentiated by engineers versus designers
The Evolution of Useful Things
by Henery Petroski A chapter discusses what industrial designers typically do for clients
Turn Signals are the Facial Expression of Automobiles
by Donald Norman -a cognitive psychologist Discusses empathy in design
Creativity: Flow and the Psychology of Discovery and Invention
by Milhalyi Csikszentmihaly-a psychologist Discusses the dynamics between creators and what is created
Addiction By Design
by Natasha Schull A sociological perspective of casino design