Default account in Mail operates differently across Apple Devices

I have three Apple devices M1 MacBook Pro, iPad 4th gen and iPhone 12pro, and the definition of using the Mail Default Account changes depending on which device I use.

I have two main accounts set up on all devices let's call them Account A (default) and Account B

I simple terms if i am using the OSX system and i wish to compose a new message apple mail implementation on OSX will always use the Default account (Account A) mail address to send the message as set up in the Mail Settings. this is regardless of what inbox or message is previously selected within mail prior to selecting New Message ( this is the important piece)

If i go to either my iPad or iPhone and do the same thing then the Default Mail account is only used if I happen to have Multiple Mailboxes selected or be reading an email within the Default account.

If you are reading an email within Account B (in my example ) or have Account B selected then Mail on IOS does something completely different to Mail on the OSX system, mail ln IOS will not use the default account to send the mail in this situation, which in my opinion is completely inconsistent and wrong.

After all a NEW Message is exactly what it says, and should not be assumed to be linked in any way with what the user was doing previously, and after all the user may have not been using the iPad or iPhone for some time before going back to generate a NEW Message

Apple get this long-running issue sorted, please?

JohnW