The AIM says pilots SHOULD advise ATC prior to any altitude change when
operating OTP.

Sorry if I'm missing something, but aren't we talking about two different
flight modes here?

No, just one.

Over the Top is a VFR flight mode. You are not under IFR restrictions.

Not this one.

VFR On Top is an IFR clearance. You are under IFR restrictions and must
report changes in altitude (among other IFRs).

This is the one we're talking about. I think Steve is pointing out the
distinction
between my use of the words "required to", your use of the word "must",
and the AIM's use of the word "should" (AIM 5-3-3).

--
Cheers,
John Clonts
Temple, Texas
N7NZ