10mg with 200mg of MDMA should give intense experience, 15 - 20mg and it's very intense. Normal or high dose of MDMA plus dose of 2c-b I would consider waaaaay too low by itself gave me a really nice experience a few times I did it. If someone is not looking for flip combo but just to enhance MDMA a bit, than only a few mg should do it, like about 5mg of pure HCl with your normal dose of MDMA. Even those who are doing it as a flip combo should, at least first trying it, significantly cut their normal dose of either 2c-b or MDMA. And I suggest trying both, low dose 2c-b with normal dose of MDMA and normal dose of 2c-b and low dose of MDMA and slightly lowered dose of both. So from there one can go to further tailor it to their liking. And same for timing, some prefer one first, some second and some at the same time. I usually took them together or spaced no more than an hour or two but intenser come up than when spaced more isn't for everyone. Sometimes I would redose 2c-b. Have in mind that how you space your doses also changes how much of synergy and potentation there is. So while a few mg of 2c-b at the same time as MDMA, or even better adjusted for come-up, will do wonders, taking such a small dose after peak of MDMA would be a waste or maybe even not pleasant.
Since first time I took this combo I liked it much more than MDMA alone. I even liked it more than candy-flipping as I like LSD better without MDMA.