Hi Joel,
Nice to meet you.
In fact, "Mid Cable Splice Enclosures" are widely used in a lot of telecom network deployment projects. We have modeled one in our sample data for reference. Please check the bookmark for "Mid Cable Splice Distribution to Access" shown below:
You could investigate the cable itself, which is in fact a continuous cable without a device splitting it into two. The Mid Cable Splice Enclosure is snapped directly on the cable, where all the splicing activities are happening on the strand, chassis, and port level (non-spatial object).
So to your first question, in a 108-strand fiber cable, where you make a mid-span cut to take out 60 strands; the rest of the segment will have 60 abandon strands (need to be created and contained in the cable), so the total number of strands now is 168 = 48 Active Pass through + 60 Active to be spliced + 60 Abandoned.
Please see below for the concept. And you also have to create internal connections with new connectors added to the edge within the device to facilitate the network connectivities. Please check this link for visualization (https://experience.arcgis.com/experience/d307f8c5fc644185a5fdf82fb9f849eb/page/page_0/?views=view_2).
To your second question about calculating the "% along distance field", we currently don't have any Out-of-the-box solutions to provide the distance from the device to the mid-span cutting point. So doing it manually would be the only sufficient alternative for now.
We will keep this in mind and see if we could implement some enhancements in the future regarding this ask.
I hope this is helpful, and let us know if there were other questions and comments.
Junjie