I used to shoot silhouette when I was younger. No hardback coats in that game. It is the only game that might give some insight to your question, but even then it doesn't really answer it.
The shot was a hit or a miss based on knocking the plate down, so no resolution in terms of central accuracy like in SR. Silhouette is a naked offhand game in terms of clothing, but is nearly unlimited in terms of the gun, trigger and scope compared to SR. So, it is still difficult to use as a direct comparison.
Some of the answer to your question is going to be rare because no SR competitor is likely to want to give up points in any serious match to find out.... maybe as an academic exercise to play with theory or technique, but the results are a foregone conclusion. The score will be lower in a club match because of the fatigue factor by the time you take shot 22.
The scores will go down when the sample is large enough to be valid, but maybe a short string of say 10 shots it may be possible to equal the performance without a coat. I can tell you without any doubt that the hardback coat works, I just can't put a definition to what you might call "almost" or how many points it is worth.
Maybe someone with a SCATT is willing to plot a few with and without samples of their hold to illustrate the difference. In silhouette, we shot 5+5 per string at each distance in most venues. So the fatigue factor is different between the two games, not just the equipment rules.