No, it's not meaningful to express it as a ratio.
The best insulation is deep insulation everywhere.
You also need to consider convection losses, and your ventilation strategy.
The attic is usually targetted first, for a combination of several reasons. It's cheap, it's easy, and heat rises, so thoroughly insulating the attic cuts down a lot of conduction losses and convection losses.
What the next-easiest intervention is, will depend on the individual property.
Upgrading from single-glazed windows to triple is often the next best, because not only does it cut conduction and convection losses, it brings improved security, and acoustic insulation too.
You can get very cheap thermal camera clip-ons for mobile phones now, so you could do your own thermal survey on a particularly cold, windy day, to find out where the cold's getting in (and thus where the heat's getting out).
Interventions on floors and walls tend to be expensive and disruptive, unless you have masonry cavity walls that can be injected with insulation material.
If you're going to insulate your home properly, then you're going to be doing all surfaces anyway. At this point, you'll want someone to come in, do a site survey, and offer you a full specification that treats the house as a whole system. Look for passivhaus-certified architects.
