Heartbeat at 16 weeks still very low?

Jennifer • Married 10/4/14 SAHM with 2 girls❤️

I have a home doppler and listen to the baby’s heartbeat every few days. I have noticed the farther along I get the easier it is to find but it’s still very low. I find it every time around my c-section scar. Shouldn’t it be moving up the farther along I get? Is it normal to be this low still?