In doing some work recently on Moxons I noticed that some of the online calculators that are available gave differing results for the same freq and wire type. Digging around, I found a recent post (Jan 2021) on worldwidedx.com by WD8DSB that explained why - there are coding errors in the calculators produced by W4/VP9KF and KG4ZOW. The Moxgen programme of AC6LA does not have these errors and results match with EZNEC.
It’s also worth noting that several of the calculators specify the wire type as AWG (American wire gauge). This is slightly different to the British SWG (Standard wire gauge). There are conversion tables on the net.