3.8mm travel, not actuation point. I don't think there is a spec from PFU of the actuation point for any model of HHKB.
It's literally right there in the article that I linked.
There's specifically has a chart towards the middle-end comparing HHKB and the R2.
HHKB Type-S / Realforce R2
"押下判定の深さ" 3.8mm vs. APCにより以下から選択可能 3mm, 2.2mm, 1.5mm
"押下圧" 45g vs 45g
The first one was translated to 'Depth of decision to press' and should refer to actuation point since it's listing the R2 actuation points, not the travel (unless it somehow means one thing for the HHKB and another for the R2, which is impossible since it's a chart).
The second simply means 'pressing force' and obviously means that they're both 45g.