Hello, HomeDepotCustomer. Thank you for contacting us at Delta Faucet. I apologize for the issue you are experiencing with this Delta Faucet RP5648 2-1/8 in. x 8-1/32 in. Plastic Bathroom Sink Pop-Up Stopper in Chrome and I understand how frustrating it can be, but am happy to help you.
To ensure the horizontal rod can fully engage the stopper allowing maximum water drainage you will want to make sure the holes on the bottom of this stopper are facing the faucet and not towards you when placing it into the sink. This can cause the stopper to not pop up far enough when pulling up the lift rod.
Please contact us directly by phone at 1-800-345-3358 or email at customerservice@deltafaucet.com if further assistance is needed at this time.
Best Regards,
Tim