Not enough hot water from Baxi 105 HE !?

DHW outlet from boiler feeds bathroom and kitchen.All pipes run thru loft / cavity and are insulated. Kitchen is further away yet water is 11 degrees hotter than bathroom at 12 litres so not getting full 35 degree rise.
Also using MIRA Fino mixer shower but to get a hot shower, have to turn pressure right down defeating purpose of having supposed pressure shower. Mira say too much water going thru boiler too quickly so have turned DHW outlet on boiler down to about a quarter but no real improvement. Shower company blaming boiler, Gas Board blaming shower. Any ideas/solutions would be appreciated.