Rare mod drop rates

I'm starting to believe that there is an upped drop rate on rare mods for those who spend more money. A lot of my guildmates are getting clumps of 5-6 mk5-A mods within a few minutes from the 100 crystal refreshes and double drop. That's probably a third or a quarter of what I've ever had drop. I've ended up putting in some money (minnow) over the last few months but admittedly not as much as these guys.

I think it's fair that bigger spenders would be rewarded but it would be nice to know if there is any truth to there being a correlation. It's pretty shocking to see when some players don't ever seem to get the rare mods to drop. One of our big spenders just had 9 drop from the 3 refreshes.