Optimal Node Placement - Long Apartment

Hello, 

I live in a long NYC apartment and the modem connection/gateway eero has to be at the north end of the floor plan above in the Living/Dining Room. The internet connection in our home office has been very weak despite getting 1 Gig speed test results from the gateway eero. Any tips or ideas for how to improve this set up? The other two nodes are marked in red above