Is there a reason that note spacing or layout changes compress single bar rests when the bar count is not shown, but seemingly don’t when the bar count is shown? Or perhaps said another way, is there a reason why having the bar count shown makes single bar rests behave like multi-rests?
I’ve tried just about every combination of numbers in the Spacing section of Multi-Rests to counteract the following, but what ends up happening is that single bar rests with the count shown tend to be awkwardly longer than larger multi-rests in compressed scenarios, instead of all rests being compressed proportionally.
Apologies — I’m going to do something I know I shouldn’t, which is bump this.
I don’t think I worded this very well initially. I’m including a GIF below:

Why does showing the “1” count make single-bar rests utilize so much more space by default?
It seems to be entirely related to “Bar count for single-bar rests.” For instance, setting single-bar rests to show as an H-bar but not show the bar count gives single-bar rests ordinary spacing (even though, ironically, they still do show the bar count, since it’s an H-bar). But if you turn on the “Bar count for single-bar rests” the spacing explodes again.

Dorico treats multi-bar rests very differently to regular bar rests. Once a bar rest shows a bar count, it’s a multi-bar rest, so a single bar’s rest can either be a regular bar rest (if the bar count isn’t shown) or a multi-bar rest (if the bar count is shown).
Single bar rests are spaced according to their rhythmic duration, per the settings on the Note Spacing page of Layout Options, or the prevailing note spacing change. Multi-bar rests are spaced according to the options on the Rests page of Engraving Options.
I agree that it would be good if single-bar multi-bar rests were spaced more like a regular bar rest. This is something I imagine we will revisit at some point in the future.
Thanks Daniel — after much finagling I did manage to get close to what I was looking for by setting “Minimum width of multi-rest” to 1, and setting the rest of the numbers in this section more-or-less normally, so that it still scales linearly without all multi-rests becoming wildly compressed.