I don't think the short seat tube extension is size-related, but I can't explain why the ti models were a more conventional shape, especially as the sloping top tube was Kona's trade mark. It's also a puzzle why the 93 and 94 brochures show the Hei Hei with a normal Kona shape, but the only photos I have from those years show a short extension, as per the 95 and 96 brochures. I have no photos prior to 93, so I don't know what shape the bikes actually were then, but the 91 and 92 brochures showed a Kona-style extension.
The bike in the 1990 catalogue is a puzzle. It appears on the Brodie page, but it has a Kona decal. The text is quite cagey, saying that Joe Murray designed it but also that Merlin 'invented' it, but not that they built it. But it looks uncannily similar to the bike in the 1989 Merlin brochure, even down to the rear XT U-brake (the other high-end 1990 Konas had moved on to cantis). If Joe Murray really did design that bike, why the U-brake and why the completely different Joe Murray design for 1991?
The bike in the 1990 catalogue is a puzzle. It appears on the Brodie page, but it has a Kona decal. The text is quite cagey, saying that Joe Murray designed it but also that Merlin 'invented' it, but not that they built it. But it looks uncannily similar to the bike in the 1989 Merlin brochure, even down to the rear XT U-brake (the other high-end 1990 Konas had moved on to cantis). If Joe Murray really did design that bike, why the U-brake and why the completely different Joe Murray design for 1991?