FWIW - lately my DS (also 18mths) has been fighting going to sleep at night - he's been going to be anywhere between 7 and 8pm with LOTS of help.
However, he's not been wanting to feed to sleep to start with - feeds for a bit then wants to get up and run around & play some more. I've (&DH) have ended up having to put him in his cot for 5 min or so and put up with the crying/screeching and then get him up to feed him to sleep properly - will feed to sleep properly - not interested in running off halfway through the feed. I don't like having to do it this way but it seems to be the way he wants to go lately

For awhile there he would go to sleep without feeding to sleep for DH at night but not every night so I was starting to think he might be starting to sleep without the feed to sleep but lately we've gone back to total feed to sleep at night.

DS goes to bed easier if he's had a longer sleep (or total sleep) is more than 1 1/2 - 2 hrs during the day. Mind you if he goes to bed near 7pm we're up around 6 (even earlier - 5:15 the other day) so I'm starting to think I need to push back bedtime to around 8 or later