I'm looking for the regulation or TC on MPs standing at attention or parade rest while under arms on duty. Which TC/FM should I check?

So far I have checked through STP 21-24-SMCT, TC 7-21.13, Military Police Leader's Handbook FM 3-19.4 and Soldier's Manual MOS 31B STP 19-31B1-SM.

I am all well aware I need to salute an officer as per customs and courtesies. Yes on occasion the salute may be delayed as we deal with an immediate situation that makes it impractical/unsafe. The question I've been looking at is while on duty as an MP, is there an FM, AR or TC that specifically addresses MPs and if we are to stand at attention or parade rest while talking to an officer or NCO while under arms and on duty.

For officer safety, I believe the answer is no, my squad leader also agrees with this assessment. I've heard other NCOs use the reason that we do not stand at parade rest/at ease or attention is for officer safety while we've been down here as well. We have not been questioned about this where we are after giving the answer that we are not standing at attention/parade rest because of officer safety and weapons retention. I have yet to have any higher ranks upset because of this, but wanted to find what written doctrine there is on this if any.

I have always been taught to salute, but not stand at attention or parade rest while on duty if we are under arms on duty as MPs, but after training today we decided to look into this a bit more and check for actual written doctrine/FMs that give clarity if there is anything specific to MPs on duty for this. Keeping in mind I did not see anything in either the MP leader's handbook or the MP handbook addressing this. It may be possible I was looking using the wrong search words.