Between 0.8 and 0.9 usually. If you're efficient it will be closer to 0.9, where efficiency is defined by the carry over tothe classical lifts (SN & C&J). It's a measure of how closely your FS resembles your BS, the more foward lean on BS the closer it is to 0.8 and the more upright the closer it is 0.9. This is a rough heuristic of course, there are exceptions to the rule and several confounds, eg depth. .. some ppl do very shallow FS, some do very deep FS .. whereas BS might not be the same depth, more depth doesn't necessarily mean less weight, some ppl get more bounce out of the hole with depth and can lift more weight, some lift less weight the deeper they go etc.
IF you use both lifts in training your ratio will be more true. If you never do a FS and test it out, of course you wont be very good at it, there is a huge technique component to it, not to mention form strength (which is how good you are maintaining good positions).
Another thing is doing a lot of FS is a waste of time, better use of time is using the BS for volume and the FS for low reps & volume .. this way you get the benefits of building whole body strength with the BS which doesn't suffer to the same degrees as FS as you do more volume .. and it carries over well to the FS so long as you're practising it regularly.
