How to improve the Bluetooth range of a DALI system with Casambi modules?

I'm having a big problem with the range of Bluetooth modules fitted to lighting fixtures in a hybrid DALI system. There are Bluetooth modules connected to the DALI controllers that act as gateways to communicate with the switches and lighting (Casambi system). As is typical with DALI, each module supports up to 63 devices (64 on each 'leg' counting with the gateway). The module is mounted in the ceiling in the vicinity of the group of devices from which it collects data. And this is where the problem arises. The light fittings usually have metal housings which block the signal from the modules mounted in them, but it is difficult to do anything about this. I took apart one of the modules used as a gateway and it turns out that the Bluetooth antenna is a thin path on a circuit board of max. 1x2cm. The range I manage to get at the moment is about 10m. Is there any point in testing with an external antenna and what type of antenna would be best? How much range improvement can be expected. I would be grateful for any advice.

BT operates in the 2.4GHz band as do routers - you could try it with one.

How do you imagine attaching an external antenna or socket to it ?
Losses due to wave mismatch can be much greater than the gain of an external antenna.
You mention something about metal fittings. An antenna on a laminate should not be close to metal parts. The spacing should be at least 3cm.
The metal box will of course attenuate the signal very strongly. In this case, putting the antenna outside can significantly improve the situation. Even if it is not matched. However, it is difficult to advise without seeing how the whole thing looks.
The general principle for achieving a long range is to ensure the so-called optical visibility of the antennas.