A 26-15 victory over Cardiff Blues on Sunday was their sixth in as many league games this season, with a positive points difference of 99.
Glasgow Warriors had headed into the weekend top of the pile but a 29-9 defeat at Ulster's Kingspan Stadium on Saturday left the door open for the Ospreys.
And they took the opportunity, Dan Evans and Rhys Webb each dotting down while Dan Biggar kicked 16 points to clinch a second Welsh derby victory of the season.
But Tandy, whose side missed out on a place in last season's PRO12 play-offs, insists he is not prone to exaggeration when assessing his side's start to the campaign.
"It's a great start for us, but a start is all it is," he told Wales Online.
"To end this block with six victories is something really pleasing. We know there has been a lot spoken about people writing us off and then all of a sudden we are a fantastic team or whatever. Somewhere in the middle is about fair.
"We are getting better. There are patches that are real good for us and our young boys are improving week in, week out. There will be a lapse at some point, but it's nice that six games in we are still unbeaten."
And, after flying out the blocks on Sunday before fading slightly in the second half, Tandy believes there is still plenty to work on in the coming weeks.
"We feel we have burned a good few opportunities and weren't ruthless enough," he added. "To concede two tries at the end doesn't represent where we have set our standards.
"We set ourselves the target of being better every week.
"It was great to see a young group, who are still learning, disappointed with conceding two tries and bombing one or two themselves."
Click here to see the best images from Sunday's Welsh derby
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