Interesting how the lengths match. It does look like a design decision.
Is the purple pen really a PG Slim? That’s supposed to be 110mm uncapped, but here it is much longer.
Btw, have you tried a Sailor medium and/or medium-fine nib? I’m wondering how they are.
(My only Sailor writing experiences are with the cheaper 1911 Young (somiko) and High Ace Neo. The €12 High Ace is a winner imho).