Я не знаю на какой длине линии будет работать клиент. Посему PROP_SEG может меняться от 2Tq до 12Tq при NBT = 16Tq.
Что будет правильно PROP_SEG = 2Tq или 12Tq (или еще чего исходя из нижесказаного)?

При этом в NMEA200 (под него ваяю) сказано:
Backbone length – 200 meters.
• Bit Rate = 250K BPS (Bits Per Second)
• Bit Rate Timing Accuracy = or better than 0.5% over temperature and life
• Sample Point = Between 85% and 90%
• Sample Mode = Single Sample (see Note 1)
• SJW = As large as appropriate (see Note 2) = Tseg2 / Bit Period

Note 1 – Although J1939 supports “2 of 3” sample mode, some CAN controllers (e.g. C167, etc.) do not support this
feature. Because analysis does not exclude either sample mode and because NMEA wishes to allow the maximum
number of controllers, the “single” sample mode is recommended.
Note 2 – Larger values of SJW, which control resynchronization timing, maximize the ability of a CAN controller to
adapt to the expected oscillator variance across all other CAN nodes. Depending on the main CAN oscillator
frequency, selection of the SJW value is not trivial. Additional material may be found in Philips application note
AN97046 "Determination of Bit Timing Parameters for SJA 1000 CAN Controller" by Egon Johnk & Klaus Dietmayer

По этому самому AN97046 выходит SJW = 2Tq и PHASE_SEG_2 = 2Tq.