For BPL to NGP:
Overnight Daily Rajdhani and a garib rath is present.
(18238),(12648,12808),(22645,12591,12511,12521,125 89),(02126),(18244,18246),(12626),(15015)
Braces show same time slot running. So daily 3-4 overnight , plus Rajdhani and garibrath are there.
For...
more... NGP to BPL:
(12645,12643,12803),(22415),(18237),(12807).
You are saying 18237 has slow TT , but this Slow TT is a boon for NGP-BPL travellers. Perfect 10 pm boarding from Nagpur and perfect 6 am de-boarding at Bhopal with sound sleep. Everybody prefers this. Also same is with samta express which has good berth multiplexing history.
Sorry. I think you have to extend it somewhere on either sides. I am giving red.