I see your point, Rayjay, especially about the full chest. Reidi do tend to be slimmer. I have seen young reidi with spines. Morphology is quite variable, but I am not sure to what extent among geographically separated reidi population.
I based my shoot from the hip ID guess on the snout length, which seems to me to be a trifle long for erectus. But again, there is a lot of variability, within and especially between populations. It's possible that this fish is neither a reidi nor an erectus. If it's a young fish it's especially hard to tell.
I'll be in Dominica and the Saintes 10 days from now, at the peak of the reidi breeding period. I'll be doing some deep diving with mixed gas, so I'll not see any seahorses most days, but I'll also do some shallow water snorkeling just for fun. I'll take my little submersible Canon point and shoot. I'm not a good photographer and I'd rather look at things than try to take pictures, but Ill try to get some close-ups of reidi. I always see them there. The population in Dominica seems to my inexpert eye to be larger and more boldly marked than reidi from the Major Antilles. That's only a casual vague impression. If I get a few shots and if they are any good I'll post a couple when I get back in late March.