If the pension increase is not staged, then those whose birthday/retirement date is soon after 6 April will get the maximum increase the following April.
I have not done the sums to see if the loss of pension from retiring early is offset by that extra increase, but somehow I doubt it will be.
If the pension increase is staged, then most likely the best date will slip from the April date to immediately after the stage increase given that the staged increase more than offsets the loss due to the time calculation.
In my case I lost out twice because my obligatory retirement date was just before the staged increase to complete the year's pay award. I would definitely not recommend being caught like that if you can avoid it.