AdT, sorry it took this long to get back to you! I read up on Surya and Reshma creams (and powders), and did a little more research on henna in general.
Surya cream often contain very little henna (lawsonia inermis is far down on the ingredients list), plus some other ingredients in it are drying. Wasn't able to locate an ingredients list for Reshma cream, even on Amazon. Have to wonder how much actual henna is in that too. Maybe you know the answer to this already. Anyway, if the creams you were using were so Henna-weak, it makes sense that it would be a gray coverage fail.
In perusing various forums, the one approach people consistantly raved about for gray coverage with toned down red, was the use of some combo of henna and indigo. Some people also added amla or cassia to their mix. Also, not everyone did the 2-step process. Some just mixed it all together (which means the indigo likely demised before it had a chance to work at full strength). I think the 2-step process is probably more reliable, but strand tests are good for figuring that out, of course.
Whenever I've had complicated questions about henna, indigo, amla, etc., I've gone ahead and called up the folks at Mehandi.com. They seem to have more knowledge about these things than the Henna Sooq people IMO. ... But to be fair, I only once spoke with a Henna Sooq rep, so my view is a little narrow. I've spoken to the Mehandi folks about 5 times lol. Anyway, that might be worth your time if you haven't already figured out what you'd like to do