Web Panel right side for JIRA Cloud plugin gets wrong height in Safari

we have an Cloud Plugin that defines a web panel
with a height of 100%.

When this panel loads in Safari the height is not calculated correctly:

The summary panel on the right hand side is cut off.
The cause is that the iframe shown in the developer tools has a height of 40px.
JIRA somehow seems to determine this value dynamically, the source code for the iframe embedding delivered to the client just contains the 100% height-value:

When this runs in chrome the height is set to 77px which display correctly:

How can we influence the height that is automatically calculated?

Thanks in advance! (PH-132)