Welcome to the TMU Forum ! Thanks for your question.
When a wider quilted pattern on top of the mattress is narrowed, the result will be a more firmer feeling. It would be most difficult to offer a “quantitative value of degree of loft/ cushioning lost” as there are many configurations to mattress covers; ultimately, it is about your individual PPP/ Pressure relief, Posture and alignment, and Personal preferences (read more here of Phoenix’s post #46 here.
Have you reached out to the mattress company regarding the different fabrication you received? Would be curious to know their response. Hope goes well and keep us posted.
! Thanks for your question.