Our Red Devil paint shakers at work would take about 10 minutes to completely put the product into suspension. It must be totally dissolved before you add it to the clear or you are just adding solvent. Depending on what clear you are using the ratio you wrote would at best give you a semi-gloss finish. To approach flat it is not uncommon to use 1:1. Also be aware that usually when flattening a product the ratio of catalyst to clear will change. You are only catalyzing the clear resin - not the flattener. That can also bring the gloss up. Keep the coats light without getting dry, that works well for maintaining the desired flattness. When wet coats are applied the flattener can settle out of the film ( just like in the can ) resulting in a higher gloss when dry.

Regards,
Dan
www.gocolours.com

FYI, the above link is to my company website. If you click there find the PPG Platinum button, follow the link to the PPG Refinsh site and there you will find all the product bulletins for everything PPG.