click this
link and scroll down to the fifth post. In your case you want to be looking at the power levels in the downstream and upstream tab. You can use the ones in the screen dumps as a guide because they are pretty much perfect. I do believe that when you put the splitter on you'll see the power go down so it might go from something like +1 to -2. There might be a corresponding increase it power on the upstream and it might go from +45 to +50. In both cases both changes are within acceptable limits.
If you fancy playing around to see what difference it makes you can take a look at the levels now, then with the splitter at the two locations you was thinking of and see how much of a difference it makes. It will be handy to know because if one of them doesn't work, you know what you can fall back to.
As an fyi, if your shub is in router mode you want to go
http://192.168.0.1 and not 100.1