About the 'linear' loading here is what happens:
when picture loop starts fastloader reads sectors: 09,0a,0b,0c,...,07,08... and so on until re-seek to track 1,
on the second loop sectors are read: 0a,0b,0c,0d,....,07,08,09... then seek again to track 1,
and yes, you guess it
After approx 2 min the reading order become 'linear' i.e.: 00,01...., 0d,0e,0f and next re-seeks don't break this linearity.
Very interesting behavior and nice example of what 'skew' means
The emulation in Oricutron is very far from perfect, I added it to be able to run DOS-8D and some interesting old software and until now there was no demand for something better, but this will change and I think to add NIB support, which will provide as side effect the possibility to use any interleave. Also I think to add support of images with more than 35 tracks (maybe fixed to 40 and 80), my opinion about sectors is to leave them fixed to 16, still thinking how to implement emulation of double-side images... any ideas are welcome and highly appreciated!