Hi,
I can confirm this on Thursday as my wheels are being built but I have 194mm Asahi spokes for Araya 7X 20 x 1.75 to sealed bearing suntour low flange hubs, and according to the guys I bought them off, they need to be laced 4 cross.
I'm not sure if the wheel width matters, just the diameter so the spoke length for 1.75 and 1.5 should be the same.
If you're interested, I have some used chrome (i think) spokes for 20" wheels fitted to a low flange hub - just came off the wheels today and come complete with sliver nipples. They look mint.