That sounds high for a trials bike, but again, it's certainly possible depending on port timing and other factors. Which highlights the reason I'd rather not take a guess at what my bike should be. If it's 'supposed' to be 12.5:1 and I make it 10:1, it'll likely still be as sluggish as before. And if it's 'supposed' to be 9:1 and I make it 11:1, it'll probably need race gas to prevent detonation.
For reference, the 2023 Betas are shown as 10.6:1 for the 300 and 9:1 for the 250. It's a bit unusual because smaller displacements are typically run with more compression, not less, but it sounds like Beta is specifically tailoring the 250s as a more beginner friendly option. So that may be why it's less than the 300. https://www.dirtrider.com/story/dirt-bikes/beta-trials-bikes-first-look-2023/
The 2023 GasGas is reported at 10.4:1 for the 300 and 11:1 for the 250. https://ultimatemotorcycling.com/2022/07/13/2023-gasgas-txt-trial-lineup-first-look-11-fast-facts-61-photos/
But that's pretty much all the concrete data I've found regarding compression ratios in trials bikes. Considering how readily available this info is for enduro bikes that I spend most of my time on, I've found this quite surprising.
Yes, I'm in the USA. If I understand correctly, our pump premium / 93 octane is equivalent to your 98/99. I've never met anyone running higher than 93 on a trials bike, as the bikes still make plenty of power at factory compression ratios / on pump gas.
Not fixing the squish isn't an option. Removing 0.5mm of squish clearance on my enduro bike made a substantial improvement. Considering that this bike needs >1.0mm of squish reduction, and that fixing the sluggishness of this bike was my primary reason for tearing it down, I'll definitely be bringing it down to appropriate levels.
But, I'd rather not fix one issue (squish) and create another (compression ratio). It'll be easy to address, if I only knew what it 'should' be.