Well I found an old school lead Duracell Ultra Gold 34N with 800 CCA for about $150. Not AGM but still... height listed as even 8".
Battery Equivalents website lists Group 35 as having same measurement as Group 25.
Group 25, Subaru OEM is L 9 1/16. W 6 7/8. H 8 7/8
Group 24. L 10 1/4 W 6 13/16 H 8 7/8
I think Subaru puts the smaller choice in to save money but the larger tray gives the option to upgrade aftermarket.
So if this is the case, I'll upgrade to the 34.