This question got me thinking.
Your values x and y represent gaps which convey different meanings based on sizes relative to each other.
I'm sure there's not an exact, scientifically proven, and precise multiplier for y, but I started thinking about other web design elements that rely on relative sizes to express meaning.
The first thing that I thought of was headers. Their meaning is entirely defined by their sizes relative to each other, so these sizes have to differ enough for users to detect.
Looking at the W3C's defined default header styles, I figured the scale between each
h* elements to range between 1.17 and 1.33, with the average of each size increase to be ~1.23.
So that's where I'd start with your visual design. Try adding 20-25% more spacing between groups, and see how that feels.
Ultimately, you're designing for humans, and human perception is not an exact science and varies from person to person. There will be people who can notice an extra 10% padding, and also users who fail to notice an extra 40%. It's all about trying to make it work for the majority, and providing additional assistance when possible (meaning, if testing proves this to be difficult for many users, you may consider a "high contrast mode" or similar setting that actually draws boundaries between implied groups).