Bluetooth range

Hello Everyone

I had made a project to send sensor data from one device to another using hc-05 Bluetooth.
i had covered both transmitter and receiver in two different aluminum enclosure, but i faced problem in pairing the when enclosure was closed for both transmitter and receiver and kept at 7 meters range, devices were not pairing. then i removed removed device from enclosure then it got paired. so i thought signals are getting weak if i keep Bluetooth in enclosure.

can some please suggest me which type of Bluetooth i should use, it has to connect/pair with other at minimum range of 10meters.

I was also thinking to use Bluetooth with external antenna. so please suggest me the best solution and please correct me if i am wrong.

I saw HC-12 is good can someone who has used HC-12 for long range tell me how it worked and i can use for my project.

Thank you in advance

bmg1234:
aluminum enclosure

Surprised you get a connection in the first place.

Regardless of what type or radios you use, putting them in metal boxes will severley limit their range.
Can you use plastic or some non metal boxes?