Tl;dr: Can I add Reaper Anti-Shine Additive to Les' Magic Wash without causing any problems? If so, how much?
Full Question: I like Reaper's Wash Medium, but I go through it pretty fast and was looking for a cheaper alternative. I've mixed up some Les' Magic Wash (roughly 50% Liquitex Matte Medium, 45% distilled water, and 5% Liquitex Flow Aid) to try as a cheaper alternative. It works well, except for one problem: Despite the 50% Matte Medium, it doesn't cut the shine on inks, especially my Vallejo Game Inks. Whenever I use it, the washed area turns glossy.
I know that a matte sealer is supposed to cut the shine, and it does to some extent, but I've never been able to successfully restore a glossy area to the extreme matte I'm used to from Reaper paints. I'd say it ends up more like the satin finish of Army Painter paints, and I don't care for it. I use both Krylon UV Resistant Matte and Testor's Dullcote to seal the minis (often a combination of the two) and have the problem with both of them. I've been through several cans of each in the past six months, so it's not a bad can, either. I've read and watched everything I could find about proper Dullcote application, so whether it's my technique or I just have unrealistic expectations, I don't know, but at this point I just want to be able to paint my minis without them ever becoming glossy in the first place, because once they do, I can't bring them back to their original level of matteness.
So, my question: If I buy a bottle of Reaper's Anti-Shine Additive, can I add it to the Les' Magic Wash to kill the shine on my inks the way that Reaper's Wash Medium does? Will it cause any problems, such as undermining the surfactant qualities of the Magic Wash? If not, how many drops of Anti-Shine Additive should I add to a dropper bottle of the Magic Wash?