That might be perfectly normal, depending on a few factors. However, the position of the arm isn't really indicative of whether the derailer itself is installed correctly, but rather an indication of how long the chain is.
To determine if the chain is the correct length, what you'll need to do is shift onto the biggest cog and check the arm at that position. It should hang vertically or lean slightly forward. I prefer it slightly forward but it depends on the bike. If the derailer struggles to bend far enough forward as you're shifting onto bigger cogs, you will need an even longer chain. If, however, as is more likely the case, the derailer arm still points back even on the largest cog, then the chain is in fact too long and ought to be shortened.
Likely what you'll see is that on the biggest cog the derailer arm hangs vertically or slightly forward. That is normal and good! That arm is responsible for pulling out the slack on the chain in order to maintain chain tension, so when less chain is being used by the gears (on the smaller cogs), the arm has to pull further back to account for the extra chain not being engaged.
The installation of the derailer is really more about setting up the limit screws to block out the range of motion that the derailer can travel in, and you can't determine that from this picture. The b-tension screw is used to pull the upper jockey wheel (small gear) on the derailer away from the cassette so they don't smoosh the chain. The b-screw shouldn't be used to account for a chain that is too long or too short, ideally.