I don't think you can put a gallon ratio on pods, it moreso comes down to what areas you have to keep your pods reproducing. Even so, I have a volume of roughly 100g.
In my case, I have a rockwall with a slight gap behind it, the only thing that can get back there is my very small cleaner shrimp, about 50-60lbs or more (diy) and didn't weigh it but it was definitely more then 50lbs at dry weight. Then I have another giant 40lb rock that I found a great deal on, possibly tonga branch or looks very similar atleast, those are the safe spots for pods in the display tank (60g cube). The sump, 50g ish cube filled to 4" below the rim, has the scrubber which will be steadily producing pods galore within the next two months, caulerpa, because I like it, and a dsb of 6-8". The sump is not your typical divided up sump with baffles and equipment compartments, it's more of a fuge design where it is also a cube and has no dividers, I did this for the maximum surface area for the dsb. I have pods on the glass of both tanks by the hundreds maybe thousands that are visible, again, that are visible. This leads me to believe that I should have a big enough population to sustain a dragonet, but this is just my assumption. Like said, never had a dragonet and I've only read story's about them clearing out a population of pods, but those story's that I've read were usually ones with no sumps and if they had a fuge/refugium, it was very small.
Didn't want to create a new thread for a similar question, looking for personnel experience of someone with a setup similar to mine and if they had success or think that I should be okay. I'll probally end up doing it anyways in about a month or so, to give the scrubber a little bit more time to mature. Unless someone with experience strongly believes that this setup wouldn't work for a dragonet.
This tank was originally designed for seahorses, hence the areas to keep a steady pod population. But, our seahorses didn't eat pods for some strange reason and passed away two months ago when they started refusing to eat, but that's another topic.