It’s 75% of salary, less €8,622 in respect of the State Disability Benefit. This is done so that in the event of a claim a claimant would receive a total of 75% of their salary, inclusive of the €8,622 State Disability Benefit.
It comes in after 26 weeks. In Company X's case this is because the company would pay your salary for 26 weeks, and then the PHI would take over. Other schemes might have a 13 or a 52 week waiting period.
The reason for the 75% limit (66% on some schemes) is to avoid the possibility that a claimant would be as well off by claiming as by working, which could give an incentive to stay claiming.