Hello Nicolas
A cleaner solution would be to allow changing the size of any block with a similar button than the one on the description block.
That is what I was meaning to say. The ability to change the width of the block that contains the WYSIWYG field.
For the short term, I modified the product->form view to change the width of my custom fields as follows.
<div class="hkc-xl-4 hkc-lg-6 hikashop_product_block hikashop_product_edit_fields" data-id="fields" style="width:auto;"><div>
This works for my custom fields block. I hope you could implement the cleaner solution in future updates.
Many Thanks