On one side, decrypting the tiles of the RISE11 chip used by Raiden Fighters Jet was easier than I thought: after placing a few bits of the source data, it became apparent that the bit order was the same as the RISE10 chip used by Raiden Fighters 2.
On the other side, however, it wasn't that easy because a couple of pixel didn't want to decrypt correctly. Eventually, it turned out to be a carry that wraps around from bit 23 to bit 0. Nasty!
So I have finished decrypting the tile graphics in all Seibu games. What I will have to do next is fix how the tiles are rendered on the screen in the RISE games, because currently the tilemap layers show garbage most of the time. The above shot is pretty much the only place without graphics errors (caused either by tile banking, or sprite encryption).