flattenStrong with position

Hmm for me it works as expected, it looks like I really did not understand you.

from panda3d.core import NodePath
from direct.showbase.ShowBase import ShowBase

class MyApp(ShowBase):

    def __init__(self):
        ShowBase.__init__(self)

        all_node = NodePath('all')

        for i in range(0, 10):
            for j in range(0, 10):
                model = loader.load_model("panda")
                model.clear_model_nodes()
                model.set_pos(i*10, j*10, 0)
                model.reparent_to(all_node)

        all_node.flatten_strong()
        all_node.reparent_to(render)

        print(all_node.ls())

app = MyApp()
app.run()