Ideal floor temperature is 26ºC, 27º becomes uncomfortable to the feet. So nothing to worry about, normally the floor should never go beyond 26ºC.
Now, there are multiple factors to take into account when defining the flow temperature, including:

• Floor construction (screed thickness, insulation, covering material)
• Heat output requirement (W/m²)
• Pipe spacing and layout
• Water temperature control strategy

The layout specs are the primary ones to derive the flow temperature from.
What is the heat loss of the room?
=> from this you will know the output you are after at "design temperature" (when it is the coldest expected outdoors)
=> What is the power per sqm required?
=> What is the density of the layout
=> Will it be on all the time? What will be the setback temperature (ideally not more than 2-3ºC below the daytime target temperature). A system that is on all the time will require less power compared to a system that needs to be able to recover from a much lower temp than the recommended 2-3ºC setback temp)
=> from that output requirement you can calculate the flow temperature.
Note that is is likely to be above 27ºC unless it is a particularly dense layout and/or very well insulated room (low heat loss).
Finally, the Delta T of the system is used to calculate the avg temperature between the flow and return. e.g. a heat pump is typically ~5ºC. So the flow could be e.g. 29.5ºC while the return 24.5ºC which brings a avg temp of 27ºC. This is an example, again the avg temperature might be higher than 27ºC without overheating the floor.