There was a little bug in index connection manual. OCZ output in Delta is not a 'Line Driver' but 'Open Collector'.
Index pulse must be widened only for IP-S. In most cases servo drives has separate settings for encoder output and electronic gearing, so we configure Delta to 10000 step pulses/rev and encoder output to 500 pulses/rev then we have precise index homing without losing resolution.
Currently IP-S need index signal to be active at least 1ms. Decreasing homing speed makes index wider, so if it's not possible to change encoder output pulse number then try decrease homing speed.
Move from homing switch is already much slower, so even for 10000 pulses/rev or something like that index homing should be possible with sensible speed.
However I'm planning to improve this function with a little help of FPGA chip
Then the problem should practically disappear.
Note that all of above is only for IP-S.
IP-A has fast differential encoder inputs and there are no limitations or special requirements for index homing.
Andrew