ES2 '61 ignition timing

Now that my ES2 rebuild is finally running, I have another query.

The ignition automatic advance mechanism that came with the bike is clearly stamped 15 d.

I have set the timing at 38 d fully advanced as the books say.

At slow idle (350- 400 rpm) it fires at about 5 d BTDC.

But it reaches fully advanced at about 1150 rpm – is this correct, it seems too soon?

The ignition point starts advancing as soon as the revs pick up from idling. It fires at about 15 d BTDC at 600 rpm.

I suspect the springs are too weak.

At what revs should the timing be 38 d?

At what revs should it start to advance?

A diagram of ignition timing vs revs would be most useful – does anyone have one?