I guess it's a question if whether you miss bail of the bail bondsmen can recover 100% of the bail despite having only lost 30% of it. I bet I can guess which it is.
That's still a better deal for the bondsman, but it's also reasonable. If you don't show up for court, it doesn't seem likely that you'll show up to deposit the other 70%... But if you don't show up for court, the bondsman probably hasn't left, and they will be available to pay the rest of the bail amount.
Of course, most bond contracts say that the bondsman can begin civil recovery against you for that full amount too.