I also don't use push fit plastic plumbing, but am sure that you must use the proper inserts for the plastic pipe as it is the internal bore than can vary slightly.
I probably also have some of those tapered copper olives. The nut for them will be flat inside to hit against olive.
Anyone needing to connect to imperial 1/2" or 1" copper pipe should carry a few Conex brass fittings, because they are a slacker fit, both the fitting body and nut, as well as better quality than the cheap brass we have now. Useful also if a pipe has been expanded slightly if ice damaged.