The number does indeed get larger with bigger losses - but most of the charges also have statutory maximums (e.g. 20yrs for wire fraud) and they'll almost certainly be served concurrently. With this level of fraud a sentence approaching 10 years might be in play, but we'll have to see what the prosecutors say.

You can look up the formula in the federal sentencing guidelines. IIRC the scale of sentencing points to dollars is sorta-logarithmic

Guidelines are just that, guidelines. Judges have a lot of latitude.