How does the rank of your rater or senior rater impact a board or application, if at all?

It is what is it. Your rater and Sr rater are going to be a function of your position.

While as a 1LT company commander I was rated by a LTC, and Sr Rated by a COL. My Platoon leaders at the time with the exact same commissioning month were rated by me (their peer rank), then Sr Rated by a LTC.

As a staff CPT I'm rated by a MAJ and Sr Rated by a LTC.

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I hope someone chimes in and validates what I'm about to give an opinion on, because it's the path I'm following for myself.

In the USAR we are in a position to spoon feed our Evaluations to our raters. We can frame how strong we want our Evals to read. The easiest Eval to write is the one where the rated soldier tells me everything they want put in it. I adjust fire from there, and when given no soldier input I give the minimum GO rating I can without derogatory counseling statements.

Our career paths are spelled out in Pamphlet 600–3. Those assignments are then recommended by your Sr raters on your Eval. The completion of those assignments end up on your Officer Record Brief (ORB/SRB). Your ORB ends up in your promotion board packet.

So.......... when a board committee is reviewing packets for your particular branch promotions it's going to be much more important that your ORB has a history of you being assigned positions guided in your Branch Path in 600-3 than who signed your OER.

I think there are a lot of us USAR officers floating around out there in random positions (especially company grade) that we found ourselves in as a function of trying to keep all the USAR gears moving, and we do ourselves a disservice by not keeping an eye on the horizon and the importance of a bureaucratic system that is looking for checked boxes when we are up for promotions being reviewed by an over worked committed trying to get through them all themselves who are using regulations as their definitive path of decision making.

Being in a valid billet for your Branch/AOC progression for the minimum required amount of time, while you are also the correct rank and correctly trained for said billet and is documented on your ORB and OER is far more important than who signed your OER.

Been in for 19 years..everyone has a different perspective and opinion on what will make your file more competitive. There is no standard for us to go off of.

So what I’ll say is this…Deliver MQ performance every rated period; no matter who rates & senior rates you. An MQ from a MAJ is still going to look better than an HQ from a COL. If you look at board trends (which you should), you’ll see that those who had 4/5 & 5/5 MQs were far more likely to get promoted than those who had 1,2,3/5 MQs….so to me, they matter and rate higher than HQs, no matter what anyone tells you about “write-up” strength.

Having served on a selection board, I can say that we have very little time to assess and provide a rating for the OML.
I didn't look at the rank of a R or SR on an OER/NCOER/FITREP unless the write up sounded like a 3 year old wrote it and then it was out of curiosity.
What you actually did combined with the enthusiasm of the writer is what matters. Also enumeration is what can assist in the case of an immature R/SR profile (#1 out of 20 CPTs that I currently rate, #1 out of all Majors I have rated over a 32 year career, etc)

It varies with the board and what they are looking for.

1, It is the responsibility for CDRs to rate. XO should do it if they are temp OIC, or you are in a BN/Bde shop running under the XO. Folks being rated by o6 & higher look like they are held to a higher standard during the rating time

I initially hesitated to comment on 1LT Will C's question as my vintage, service, and changes in the promotion systems all color my response, but decided that, all that considered, my thoughts are still worth considering.
My thoughts include the fact that promotions in the more junior levels are essentially automatic unless you have a negative incident that demonstrates disqualifying attributes in either your professional performance or morally/ethical deficiencies. The most significant culling occurs when competing for selection to major. By this point in a career, your contemporaries who only remained for their initial commitment have departed and you are competing with those who are career oriented. The number of competitors has lessened and there are far more fitness reports, written by various reporting seniors, to be considered.
Exemplary and lower candidates can almost be identified mathematically and selected or passed over with a cursory review of their record to validate their position. It's the remaining "middle of the pack" that requires closer analysis. There are many variables at this point including ranking amongst peers, billets filled, and even the reputation of the evaluators who may be known by members of the board. The seniority of the evaluators is less important than the respect held for them and their performance.