I give them as much sun as I can. My roses and peonies I plant in my sunniest areas. Neither should have to compete with tree roots. Al

what about T P's, I thought some shade was beneficial.

does the beneficial only apply to the fading of the flowers ?

All peonies can benefit from some shade. TP's especially. Lactifloras are native to Mongolia so they can stand the most direct sun. However some of the others have parentage from woodland areas and do best with some shade. Think edge of woodland.

Shade can be relative since if you plant so you look up to the sky and see blue but the area is shady the plants are techically in the shade but are receiving sunlight. In high altitudes the ground receives even more of the sun's rays and plants will receive more rays.

Tree peonies in my area seem to do better when blocked from the morning sun. The reason for this is that when the sun hits the stems when it is cold the side the sun hits warms up. The side away can be still frozen. The area where the extremes hit can be damaged. If planted where there is afternoon sun the plant has already warmed up before the sun hits but the temps are starting to cool. This in my mind reduces the chance of damage to the stems since the change is more gradual. Of course when the temps drop 40 degrees in an hour, which it does in some areas, nothing will help.