ATM It happens again (ctd.)

["Arjan te Marvelde (ELN)" <Arjan.te.Marvelde@eln.ericsson.se>]

Thanks for the help so far, but i'm afraid new problems are recurring:
I have dug out the high center, passed through a very nice sphere and i am now slowly on my way to a parabola.

However, i see things go wrong now. Although i'm doing the prescribed MOT parabolization strokes, and even linger somewhat in the COC area, a central hole is developing. This is what happened in my former figuring attempt, and my suspicion is that i make a systematic error.
Can anybody help me understand what goes wrong?

Some details: 
10" mirror, 128" ROC, 3/4" plate glass, full sized pitch tool.
Foucault readings with fixed source should range from 0 in the center to +5mm at the edge. Currently the central 50% is approximately spherical, and from there to the edge ROC increases to about +3mm offset.

Thanks,
Arjan te Marvelde

PS Tonight i plan to try accentuated pressure with the tool edge on the 60-80% zones.