It think, you mixed up the import of wavetables with the creation of wavetables.
When you import wavetables from other synths, these wavetables do not contain any information about the length of the wavetable envelope, because it does not exist in other synths. HALion sets the wavetable envelope to a length of 2 seconds. This assumed length can be adjusted after the import.
When you extract a wave from a sample, HALion uses a window to extract the spectrum. These windows are much shorter than 2 seconds. The maximum length is 2048 samples. You can try this in Fixed Mode, where you can set the size of the window manually.
You could try the following:
- Switch to fixed Mode.
- Set the extraction marker and size of the window so it matches exactly one cycle of the waveform in the sample.
I hope this helps you to get the result you want.