ANT+ sensors connect only if watch is at 30cm distance from sensors

Hello all,

I installed ANT+ sensors (Megene) on my dummy cyclette.

They connect regularly ro the ANT+ dongle connected to windows PC. So I can succesfully use them with software like Zwift or Onelap.

But my Forerunner 55 connect to them only at a 30cm distance from sensors. As soon as I put my wrist on the cyclette handles the connection is lost.

How can I make the connection more reliable?

I replaced all batteries on sensors and the watch is fully charged.

Suggestions?

TIA

tony