LumenRT - flicker

When exporting movies from large scenes, I'm getting severe atmospheric flickering in the distance. It appears to be a fluctuation in the "Clear/ Hazy" setting, but even appears if I turn Hazy right down to Clear and Aerial down to 0%.

I've checked on the usual suspects;

• eg. the Wiki that states that the problem is usually due to geometry far away from the model (https://communities.bentley.com/products/microstation/microstation_visualization/w/microstation_visualization_wiki/33669/solve-flickering-issue-on-lumenrt) - I've checked this by detaching all old reference files, deleting everything that doesn't appear on the terrain, compressing the file and doing a "fit view" to be sure the model fills the window before exporting.
• with reference to the post earlier today (https://communities.bentley.com/products/microstation/microstation_visualization/f/visualization-forum-1977638070/215101/after-exporting-my-dgn-file-into-lumenrt-the-lrt-file-appear-flickering-dark-spot) - My DGN is centered at x,y,z = 0,0,0, and is only about 8km x 6km (ie. much less than the 50km we're now told is the current limitation for LumenRT.

Please let me know what else I should try to fix this.

I'll upload the DGN and LRT now.

Max