Hdr envinronment resize

sorry I would like to ask you how it is possible to reduce
the absolute dimension of the hdr in the ambient envinronment

You can’t at the moment as HDRI are infinite spherical projections. The way you could do it it by putting the HDRI textures on a sphere and flipping the normals, so you can actually manipulate the sphere. But it wouldn’t bring the lighting features.
I submitted a feature request some times ago for ground projection of HDRI, which by essence is related to what you are trying to achieve.
You can upvote my proposal and cross the fingers :wink: HDRI ground