Nik320 is on the right trail...
You Should be providing reporting points up to 30mins/200nm.
Just had this one pointed out to me recently by a checkie after 29+ years of flying, the answer is in the preface of the AIP!
To paraphrase...
Should = Recommended or advisable.
Must = A regulatory requirement.
PS: After all these years it seems I could have been doing a lot less!
