Annularis will get to 12" in the wild, but the largest specimen I've seen (even in large tanks) is around 10", so I'm basing my suggestion on that. A 10", fat, aggressive annularis angel cannot live in a 48" x 18" footprint, period. a 72" x 24" footprint MAY be ok, but that's a big if. I would recommend at least a 96" x 24" footprint for a full-grown adult annularis.
Navarchus angel will get to 10-12" in the wild, but most of the time only gets to 8" in captivity, and that will take years and years. I own one so I know. A standard 180g (72" x 24" x 24") will be a good long-term home for a navarchus, but I really wouldn't go smaller unless the tank is lightly stocked, but it'd still have to be at least a 125g (72" x 18" x 22").
Sometimes it's hard for hobbyists to imagine how big a full-grown fish is compared to its juvenile size, which is almost always the size sold in the store. To put into perspective, take a 3" juvenile Navarchus angel, multiply that size by 5, then you get the idea of how it's going to look when it's full grown. An 8" adult navarchus angel is not just 3 times bigger than a 3" juvenile, but would be around 5 times bigger because it'll gain girth as well! If your tank looks just just "big enough" for the juvenile, it's too small for the adult!
