convert h265 to h264 issue

Hi experts, I have a question about converting HEVC to H.264 format. The original video is HEVC, 4096x4096, 29.97 fps. I want to convert it to H.264 with the same resolution and fps. But the default converted size is 2304x2304, and seems if I adjust settings manually, the maximal resolution can be set to 3068x3068. It will show a "invalid framesize/framerate for this level" error message if I continue to enlarge it. How can that be and what should I do if I just want to convert the format and keep the same resolution and fps? Thanks a lot.