About IPM bev_plane heights setting

[imyyf]

VectorMapNet_code/configs/vectormapnet.py

Line 82 in 4bcc8b4

heights=[-1.1, 0, 0.5, 1.1],

Hi, we find that your model using [-1.1, 0, 0.5, 1.1] as the bev_planes' presetting heights. And your former work HDMapNet using only height 0.
But by our visualization, we find that using raw camera images as input to get BEV results with height -2 can get better BEV results(when height as -2, we can get clean BEV image with strong road semantic information, heights as yours setting the BEV image can't be found road information by eyes).
So we are curious about that there are better heights setting for IPM(for nuscenes data)?