Fiddlerman said
Not completely logical to me but perhaps when you are using those fingers and all the way over to the G string, your bow is affected as well angling towards the bridge. If the bow is too close to the bridge it'll sound scratchy.  

I have been watching myself and came to the result, that the fingerboard hand influences the bow hand if the fingerboard hand is struggling. In other words, if the fingerboard hand loses relaxation and suffers, the other hand does too. If something is painful our shoulders tend to tense and that effects both hands. That's why I find pausing very important and if the fingerboard hand is exhausted because it has been working harder on a hard to reach string, I pause even sooner and more often. It also depends on the key since those with many ♭♭♭ make it harder. Yes we have to accept our limits to avoid tension. Some may have longer and more flexible fingers than I have and I accept that. I also think we should not play too much on hard to reach strings, being moderate in using them.