Find the file Windows.xml at
E:\SteamLibrary\steamapps\common\7 Days To Die\Data\Config\XUi_Menu\Windows.xml

Add the range you want to these two lines (always backup your original files), I've added 125 and 145

<gameoption name="PartySharedKillRange" title="goPartySharedKillRange" value_wrap="false" value_type="int" values="0, 100, 125, 145, 200, 500, 1000, 5000, 10000" display_names="goDisabled" value_localization_prefix="goPartySharedKillRangeValue"/>

<browsergameoptioncombined name="PartySharedKillRange" title="goPartySharedKillRange" value_wrap="false" values="0, 100, 125, 145, 200, 500, 1000, 5000, 10000" display_names="goDisabled" value_localization_prefix="goPartySharedKillRangeValue"/>

Now when you load your existing map you can pick between the new ranges. Verified they work in-game.

If you are hosting a proper dedicated server find your way to the folder and file at
E:\SteamLibrary\steamapps\common\7 Days To Die]serverconfig.xml

Once in the file go to the line

<property name="PartySharedKillRange" value="200"/>
<!-- The distance you must be within to receive party shared kill xp and quest party kill objective credit. -->

edit the value to the range you want and save the file.