In your query, you have eval volume=recv_bytes/1024/1024 | stats sum(volume) as volume by src_ip
Remove that, and just have | stats sum(recv_bytes) as volume by src_ip
Doing the recv_bytes/1024/1024 is converting your byte count to MB and skewing your results. Leave the formatting of the values to later.
So you should have
source="F:\\Splunk_Log Files\\*" | stats sum(recv_bytes) as volume by src_ip | sort - sum(volume) | head 10
| eval b=volume | eval kb=b/1024 | eval mb=kb/1024 | eval gb=mb/1024 | eval tb=gb/1024 | eval volume=case(tb>=1,tb."TB",gb>=1,gb."GB",mb>=1,mb."MB",kb>=1,kb."KB",1=1,b."b")
| fields - b, kb, mb, gb, tb
... View more