What?"In custody" and "In custody for purposes of Miranda" are two distinct elements of law. I'm sure TM can attest to the fact that the "Lawyer's Edition's" of SC decisions have very good commentary, if you will, on cases. Although many years have passed, I believe Miranda is one of those I read. More insight than a Law Journal Article, imo. Ernesto used to sell Miranda cards, signed, for a dollar.
Miranda is 50 years of common law, so in that respect, too many feathers on the chicken to count to be 100% in agreement by every Court. Simple avoidance of to admit or not to admit as evidence, any statement made, is simply arrest/cite on the evidence. If they are guilty, they know it and have a very good idea of a plea bargain in the future.