I am sure it is not a problems with hosts in most cases but with protocol and realization (code) of current sia clients itself.
I often see very low upload speeds from host side too. While my host can receive data x20-100 times faster. For example yesterday one of the renters spent about 10 hours to upload just ~1 Gb of data to my host. Despite the fact that the host has Internet connection speed 50/50 Mbps and the network, processor and disk load were low at this time.
One of the problems - why sia renter client upload only 4 Mb of data per round of communication with selected host? I know 4 Mb is a basic unit(sector) for sia, but protocol (and default client settings) allow uploading of multiple 4Mb chunks in one round. But renter client still use only one for unknown reason. Current standard renter routine :
1 - connect to a host
2 - make multiple rpc calls to check settings and negotiate uploading conditions
3 - upload 4 Mb of data
4 - make micro-transaction (this include modify and sign contact by both host and renter) to pay host for uploading
5 - disconnect from host
6 - wait a second or two
7 - connect to a same host again to upload next 4 Mb
.....
and so on
